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Animal Biology
Mario V Balzan Ph.D.
Institute of Applied Science, MCAST
mario.balzan@mcast.edu.mt
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Objectives
• To give students a global vision of the structure and organisation
of the main groups of animals as well as their diversity, from an
evolutionary point of view.
• This unit is part of a larger unit, which also focuses on cell biology.
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Learning Outcomes
• On successfully completing this subject, students will be able to:
• Demonstrate knowledge about basic concepts for the study of Animal
Biology.
• Demonstrate knowledge about the main levels of organization and
architectural patterns of non-arthropod invertebrates.
• Understand the systematics and phylogenetic relationships between the
main groups of animals as a result of evolutionary and adaptive
processes.
• Demonstrate knowledge about the morphological characteristics,
biological cycles and ecological importance of metazoan groups, as well
as their interactions with human beings, with special emphasis on those
with more veterinary interest, such as parasites or species of economic
interest.
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Content
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1.
INTRODUCTION. Characteristics of living beings. The kingdoms of organisms and the
concept of animal. The concept of species. Classification of organisms: taxonomy and
systematics.
2.
LEVELS OF ORGANIZATION. Structural organizational levels. Animal organization plan.
Concept and type of symmetry.
3.
REPRODUCTION. Type of reproduction: asexual and sexual. Parthenogenesis. Adaptive
meaning of the different reproductive patterns. DEVELOPMENT: Biological cycles. Larval
and metamorphosis development.
4.
PROTOZOA. The concept of Protozoa. Shape and function. Representative types. Main
parasitic groups.
5.
PORIFERA. Cellular elements and structural types. CNIDARIA. Basic organization
Biological cycles
6.
PLATYHELMINTHES. Basic organization of Turbellaria, Trematoda and Cestoda.
Morphological particularities and biological cycles of parasitic platyhelminthes.
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Content
7. MOLLUSCS. General characteristics. Gastropoda, Bivalvia and Cephalopoda. Groups of
veterinary interest
8. ANNELIDS. General characteristics. Polychaeta, Oligochaeta and Hirudinea.
9. NEMATODES. General characteristics. Biological cycles of parasitic nematodes.
10. ARTHROPODS. General characteristics. Structure and importance of the cuticle. Basic
elements of a segment. Chelicerata. Mites
11. CRUSTACEANS. Basic organization. Reproduction and development. Groups of veterinary
interest.
12. INSECTS. Basic organization. The flight. Development and metamorphosis. Groups of
veterinary interest.
13. EQUINODERMATA. General characteristics
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Content
14.CHORDATA. General characteristics and basic organization.
Basic organization of Chephalochordata. General
characteristics of the vertebrates. FISH. Agnatha, Condrichtia
and Osteichtia. Basic organization. Structural and functional
adaptations.
15.AMPHIBIANS. General characteristics. Anura and Caudata.
REPTILS. Adaptations to the terrestrial environment. The
amniota egg. Diversity.
16.BIRDS. Morphological and physiological adaptations on flight.
Endotherm. MAMMALS. General characteristics. Tegument and
derivatives. Patterns of feeding and dental formulas. Diversity
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Methodology
• Master Classes: Lectures and Flipped Classes
• Seminars: Directed Work Classes (glossary of terms) and Problem Classes (solving problems, with
student presentations)
• Practical Sessions
•
•
•
•
Practical session 1. Observation and study of non-arthropod protists and invertebrates
Practical session 2. Observation and study of Molluscs: anatomy and diversity.
Practical session 3. Arthropods: anatomy and diversity. Crustaceans, Chelicerates and Insects.
Practical session 4. Chords: Fish: anatomy and diversity.
• Assessment of Master Classes (76%), Laboratory (14%) and Seminars/Problems (10%)
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Bibliography
• Hickman, C.P., Keen, L.S., Eisenhour, D.J., Larson, A. and
Anson, H.I., 2024. Integrated principles of zoology. 19th ed.
New York, NY: McGraw-Hill.
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Topic 1: Introduction
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Introduction
• ‘Zoology’ – the scientific study of animal life. It builds on centuries
of human observations of the animal world.
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Fundamental Properties of Life
• Historical Continuity of Life
• Common descent in history and fossil record to a common ancestor that
must have arisen almost 4 million years ago.
• Replicating molecular systems, which could not have produced fossils,
must have preceded and given rise to cellular life, whose history appears
in the fossil record.
• All descendants of life’s common ancestor, past and present, lie within
our concept of life.
• The most fundamental attribute is reproduction of individuals with
heredity and variation – replication of molecules that store information is
unique to life and must trace to life’s origin.
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Fundamental Properties of Life
• Historical Continuity of
Life
• Evolution – there is a
temporal continuity of
ancestral and descendant
populations but also
extensive and ongoing
change, which we refer to
as evolution.
• Led to spectacular diversity
in molecules, cells, life
forms, functions and
behaviours.
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General Properties of Life
• Living systems possess unique features:
• Chemical uniqueness
• Complexity and hierarchical organization
• Reproduction
• Possession of a genetic program
• Metabolism (e.g., cellular respiration in mitochondria)
• Development (e.g., metamorphosis in monarch butterflies)
• Environmental interaction (e.g., chameleons capturing prey)
• Movement (e.g., ciliary movement in epithelial cells)
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Chemical Uniqueness
• Living systems assemble macromolecules that are highly
complex, which obey chemical laws and enable life, example:
• Proteins: Built from 20 amino acids with unique peptide bonds
• Nucleic acids: DNA encoding the genetic blueprint.
Example: The
protein
endothelin-1,
which regulates
blood pressure
(Figure 1.2)
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Complexity and Hierarchical Organization
• Living systems are organized into hierarchical levels:
• Cellular: Macromolecules forming organelles like mitochondria
• Organismal: Tissues forming organs and systems (e.g., epithelial cells in
oviducts)
• Populational: Social interactions in populations (e.g., bees)
• Each level builds on the level below it and has its own internal
structure which often is hierarchical. Properties arise from
interactions among components. E.g.: Blood pressure emerges at
the organismal level
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Complexity and Hierarchical Organization
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Reproduction
• Reproduction ensures
continuity and diversity:
• Heredity: Faithful trait
transmission (e.g., DNA
replication with high fidelity)
• Variation: Differences among
offspring (e.g., chromosomal
changes in cell division)
• Levels of reproduction:
• Genes replicate (Figure 1.5A)
• Cells replicate (Figure 1.5B)
• Organisms reproduce (e.g.,
king snake hatching, Figure
1.5C)
• Species emerge (e.g., sea
urchin speciation, Figure
1.5D)
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Cellular
Division
Mitosis
vs
Meiosis
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Possession of a Genetic Program
• DNA encodes the information of life;
• Figure showing how the nucleotide
base sequence inside the DNA
molecule encodes genetic
information. Genetic variation is
shown in DNA molecules that are
similar in base sequence but differ
from each other at four positions.
Such differences can specify
alternative traits, such as different eye
colours.
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Possession of a Genetic Program
●
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Encompasses the
components of the
genetic coding that
structures organisms
(nucleotides, genes,
chromosomes)
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Possession of a Genetic Program
●
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Encompasses the
components of the
genetic coding that
structures organisms
(nucleotides, genes,
chromosomes)
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Possession of a Genetic Program
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Possession of a Genetic Program
GD is the raw
material on which
evolutionary
processes act;
● Genome sizes vary
enormously.
●
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Possession of a Genetic Program
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Genetic Diversity
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Metabolism
• Metabolism sustains living systems. Catabolic and anabolic
processes:
• Catabolic: Energy release by breaking down molecules
• Anabolic: Building macromolecules (e.g., synthesis of carbohydrates)
• Example: Cellular respiration occurs in mitochondria,
transforming chemical energy into ATP.
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Development
• Development describes changes
from origin to adulthood:
• Example: Monarch butterfly
metamorphosis (egg, larva, pupa,
adult, Figure 1.8)
• Growth and differentiation: Organisms
increase in size and develop
specialized structures
• Commonalities: Early developmental
stages tend to be more similar across
species.
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Environmental Interaction
• Organisms interact with their
environment (ecology studies
these interactions):
• Example: Chameleons
capturing prey with their
projectile tongues. Responses:
From simple movements to
complex behaviours, such as
predator avoidance.
Chameleons can fine-tune camouflage to the
predator's identity.
https://www.newscientist.com/article/dn13944chameleons-fine-tune-camouflage-to-predatorsvision/
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Environmental Interaction
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Movement
• Living systems and their parts show precise and controlled
movements arising from within the system.
• Examples:
• Molecular: Ciliary movement in epithelial cells (Figure 1.4)
• Organismal: Chameleons moving to capture prey
• Controlled by internal processes, enabling survival and adaptation
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Life Obeys Physics Laws
• First Law of Thermodynamics - Energy is neither created nor
destroyed but can be transformed from one form to another.
• All aspects of life require energy and its transformation.
• Second Law of Thermodynamics - Physical systems tend to
proceed toward a state of greater disorder, or entropy.
• Living cells and organisms maintain complex molecular organization only
as long as energy fuels the organization. The ultimate fate of materials in
the cells is degradation and dissipation of their chemical-bond energy as
heat.
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Organismal Diversity
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Organismal Diversity
Encompasses the full taxonomic hierarchy and its components, from individuals
upwards to populations, subspecies and species, genera, families, phyla and
beyond to kingdoms and domains.
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Organismal Diversity
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• What is a species?
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What is a species?
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What is a species?
The biological species concept essentially says that two organisms that cannot
interbreed and produce fertile offspring are different species.
● However, in many groups of organisms, including bacteria, fungi, and many plants
and animals, asexual reproduction—reproduction without sex—predominates.
● Hybridisation cannot be used as a criterion for species recognition
●
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What is a species?
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What is a species?
A zebroid is the offspring of any cross between a zebra and any
other equine.
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What is a species?
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What is a species?
Definition for evolutionary species: 'a single lineage of populations
that maintains its distinctive identity from other such lineages'.
● Abrupt changes in diagnostic features mark the boundaries of
different species in evolutionary time.
●
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Organismal Diversity
•
Construction of Phylogenetic Trees:
Taxonomy is part of a larger division of biology known as
systematics. Determination of phylogeny is a goal of systematics.
• Done by the construction of phylogenetic trees, which in a sense
represent evolutionary hypotheses and attempts to define
monophyletic groups. To build these trees, we must have data,
which comes from the characteristics used in classification.
•
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Organismal Diversity
●
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Traditional Classification: Data used in traditional systematics stresses
both common ancestry (monophylesis) and the amount of divergence
among groups. The traditional, dating to Linneaus view, is that birds have
feathers, reptiles have scales, and mammals have hair. Using this as a
major character, a classification like that above has been constructed.
Fossils, evidence of past life, are not included in this classification. Since
all of these groups have the amniotic egg, or a modification of it, they
would be united in a larger taxon.
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Organismal Diversity
●
Cladistics:
–Cladists group organisms based on
the presence of shared derived
characters, not the overall similarity of
potential group members.
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Organismal Diversity
• Homology refers to the similarity between anatomical
structures, genetic sequences, or other biological
traits in different species due to shared ancestry.
• Homologous structures arise from a common
ancestor and may serve similar or different functions
across species.
• For example, the forelimbs of vertebrates, such as the
wings of bats, the flippers of whales, and the arms of
humans, have similar underlying bone structures but
are adapted for different purposes like flying,
swimming, and manipulating objects. Homology
provides evidence of evolutionary relationships and
the concept of descent with modification.
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Organismal Diversity
• Homoplasy: the resemblance
between traits in different species that
is not due to common ancestry but
rather to convergent or parallel
evolution. This similarity often arises
because species face similar
environmental pressures, leading to
analogous adaptations.
• Example: the wings of bats
(mammals) and birds (avian reptiles)
are not homologous because their
last common ancestor did not have
wings. These structures evolved
independently to serve the same
function of flight.
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Organismal Diversity
●
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Phylogenetics: the
study of evolutionary
relationships among
groups of organisms
(e.g. species,
populations), which
are discovered
through molecular
sequencing data and
morphological data
matrices.
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Organismal Diversity
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Organismal Diversity
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Organismal Diversity
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Animals
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Animals
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Animals
• Metazoans, or Animals, are eukaryotic, heterotrophic,
multicellular organisms that are mobile at some stage of their life
cycle. Their cells, lacking a cell wall, are generally organised into
tissues with specific functions, are interdependent, and their
activities are coordinated.
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Speciation
Speciation: As populations diverge, they
form similar but related species.
Implies:
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-
Genetic differentiation
-
Appearance of isolation mechanisms
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Allopatric Speciation
https://evolution.berkeley.edu/modes-of-speciation/allopatric-speciation/
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Allopatric Speciation
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Allopatric Speciation
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Peripatric Speciation
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-
Geographically Isolated
-
Founding event. Cause: migration
-
Species are differentiated by genetic
drift and selection
-
https://evolution.berkeley.edu/modesof-speciation/peripatric-speciation/
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Parapatric Speciation
•
No specific extrinsic barrier to gene
flow. The population is continuous but
does not mate randomly.
•
Individuals are more likely to mate with
their geographic neighbours than with
individuals in a different part of the
population’s range.
•
In this mode, divergence may happen
because of reduced gene flow within
the population and varying selection
pressures across the population’s
range.
Figure >
Although continuously distributed,
different flowering times have begun to
reduce gene flow between metal-tolerant
plants and metal-intolerant plants.
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Sympatric Speciation
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•
No geographic isolation
•
Merely exploiting a new niche may
automatically reduce gene flow with
individuals exploiting the other niche.
This may occasionally happen when, for
example, herbivorous insects try out a
new host plant.
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Sympatric Speciation
•
Species: Yellow-bee Orchid (Ophrys
lutea) and Ophrys sicula.
•
Shared Range: Both species have
completely overlapped distributions.
•
Pollination Mechanism: Each species
attracts different solitary bee species
using specific chemical signals. These
signals mimic the pheromones of
female bees.
•
Speciation Factor: Pollinator specificity
reduces gene flow between the two
orchid species.
•
Outcome: Ophrys sicula was once
considered a variant of Ophrys lutea
but is now recognised as a distinct
species.
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Sympatric Speciation
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•
Original Habitat: 200 years ago,
ancestors laid eggs only on native
hawthorns in America.
•
Host Shift: With the introduction of
apples by immigrants, some flies began
laying eggs on domestic apples.
•
Mating Preferences: Females lay eggs
on the fruit they grew up in. Males
search for mates on the same type of
fruit.
•
Reduced Gene Flow: Hawthorn flies
mate mostly with other hawthorn flies,
and apple flies with apple flies.
•
Genetic Divergence: Over time, genetic
differences have emerged between the
two groups, potentially marking the
early stages of sympatric speciation.
From left to right, apple maggot flies, apples, and hawthorns.
https://evolution.berkeley.edu/modes-of-speciation/sympatric-speciation/
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Adaptive radiation of
Darwin’s Finches
Differences in size, beak, shape and
feeding habits
From microcosm to macrocosm: adaptive
radiation of Darwin’s finches | Evolutionary
Journal of the Linnean Society | Oxford
Academic
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Adaptive radiation of
Darwin’s Finches
Differences in size, beak, shape and
feeding habits
From microcosm to macrocosm: adaptive
radiation of Darwin’s finches | Evolutionary
Journal of the Linnean Society | Oxford
Academic
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Animal
Diversity
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Animal Diversity
Zoogeography: the
study of the
distribution of
animals, their
patterns and the
factors responsible
for them.
Give an overview
of the fauna in
these terrestrial
biogeographic
regions
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2. The
Architectural
Patterns of
Animals
Mario V Balzan PhD
mario.balzan@mcast.edu.mt
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The Architectural Patterns of Animals
• Although animal diversity is enormous, having a common
ancestor, ancestral inheritance limits the design of animals.
• There are distinctive characteristics of each group.
• Architecture: Basic architectural patterns of animal organisation.
• Levels of organisation (unicellular, multicellular, etc)
• Symmetry
• Embryonic germ layers and body cavities
• Metamerism (segmentation)
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Increased Complexity
Structural Levels of Organisation
• Protoplasmic level: Vital functions are found inside a cell.
• Cellular level: Aggregation of functionally differentiated cells.
• Tissue level: Similar cells are organized to carry out a
common function, forming tissues.
Volvox
• Organ level: Tissue aggregation to form organs. Flatworm
• Systems level: Organs that coordinate to perform a certain
function
Flatworm
Porifera
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Structural Levels of Organisation
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Cnidaria
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Structural Levels of Organisation
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Structural Levels of Organisation
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Increased Complexity
Structural Levels of Organisation
• Protoplasmic level: Vital functions are found inside a cell.
Protists
• Cellular level: Aggregation of functionally differentiated cells.
Some Protists (e.g. Volvox) and Porifera
• Tissue level: Similar cells are organised to carry out a
common function, forming tissues. Cnidarians
Volvox
• Organ level: Tissue aggregation to form organs. Flatworms
Flatworm
• Systems level: Organs that coordinate to
perform a certain function. Rest of animals
Flatworm
Porifera
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Structural Levels of Organisation
Complexity and Body Size:
• A correlate of increased anatomical complexity
is an increase in body size, which offers certain
advantages, such as more effective protection
against predation, reduced energy cost of
locomotion, and improved homeostasis.
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Cnidaria
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Symmetry
Evolutionary Divergence
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Symmetry
Symmetry: the arrangement of body
structures with reference to some axis or
body plan.
Leads to a balance of proportions and
correspondence in size and shape of
opposite sides.
Any organism that when divided along a
length of any plane results in two equal
parts is said to by symmetrical.
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Symmetry
• Asymmetry – the absence of symmetry
• Typical of porifera
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Symmetry
• Spherical Symmetry – any plane passing through the centre
divides a body into equivalent, or mirrored, halves. Infinite
symmetry planes.
• Occurs among some unicellular forms and is rare in animals.
Normally, floating or rolling organisms (Protists).
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Symmetry
• Radial Symmetry – applies to forms that can be divided into
similar halves by more than two planes passing trough the
longitudinal axis.
• Tubular, vase or bowl shaped. E.g sponges, hydras, jellyfish, sea
urchins. Usually, one end of the longitudinal axis is the mouth
(oral surface). In sessile forms, e.g. hydra and sea anemones, the
basal attachment dis is the aboral surface.
Cnidaria
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Symmetry
• Bilateral Symmetry - animals that can be divided along a sagittal
plane into two mirrored portions - right and left halves.
• Bilateral animals are much better fitted for directional (forward)
movement than are radially symmetrical animals.
• Cephalisation – strongly associated with bilateral symmetry.
Produces an efficient localisation of organs for sensing the
environment and responding to it.
• Cephalization is always accompanied by differentiation along an
anteroposterior axis, although the evolution of this axis preceded
cephalization
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Symmetry
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Symmetry
Evolutionary Divergence
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ORGANOGENESIS
FERTILISATION
EMERGENCE
OF THE
MESODERM
SEGMENTATION
Blastocoel
GASTRULATION
(2 germ layers)
MORULA
BLASTULA
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Archenteron (primitive gut)
Blastopore
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Germ Layer
Structures
Endoderm
- Epithelium lining the digestive tract (except the oral cavity and anal canal) and the epithelium of its glands.
- Epithelium lining the urinary bladder, bile ducts, and liver.
- Epithelium lining the pharynx, Eustachian tube, tonsils, tympanic cavity, larynx, trachea, bronchi, and lungs.
- Epithelium of the thyroid, parathyroid, pancreas, and thymus glands.
- Epithelium lining the prostate, Cowper's glands, vagina, vestibule, urethra, and associated glands.
Mesoderm
- All cardiac and skeletal muscle tissue, and most of the smooth muscle tissue.
- Cartilage, bone, and other connective tissues.
- Blood, red bone marrow, and lymphatic tissue.
- Blood vessels and lymphatic vessels.
- Dermis of the skin.
- Fibrous tunic and vascular tunic of the eye.
- Mesothelium of the thoracic, abdominal, and pelvic cavities.
- Kidneys and ureters.
- Adrenal cortex.
- Gonads and genital ducts (excluding germ cells).
- Dura mater (outer layer of the meninges).
Ectoderm
- All nervous tissue.
- Epidermis of the skin.
- Hair follicles, arrector pili muscles, nails, and the epithelium of cutaneous (sebaceous and sweat) glands and mammary glands.
- Lens and cornea.
- Inner ear.
- Neuroepithelium of sensory organs.
- Epithelium of the oral and nasal cavities, paranasal sinuses, salivary glands, and parts of the anal canal.
- Epithelium of the pineal gland, pituitary gland, and adrenal medulla.
- Melanocytes (pigment-producing cells).
- Nearly all components of the skull and connective tissues of the head.
- Arachnoid and pia mater (meningeal layers).
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• Radial Cleavage
• Blastopore becomes an
anus and a new opening
makes the mouth;
• The coelom forms via
enterocoely
• Cleavage is regulative
• Animals with these
features are called
Deuterosomes. E.g. sea
urchins, chordates.
• Spiral Cleavage
• Blastopore becomes
mouth;
• Cleavage is mosaic;
• If a coelom is present, it
is made via schizocoely.
Animals in this latter
group are called
lophotrochozoan
protostomes, and
include molluscs,
segmented worms, and
other taxa
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Metamerism (segmentation)
• Serial repetition of body units along the longitudinal axis.
• SEGMENT or METAMER = A segment or metamer refers to the
repetitive units in the body of segmented animals. These units
often contain repeating structures such as muscles, nerves, blood
vessels, locomotor appendages, and in some cases, sexual and
excretory organs.
• Only in some CELOMATES (i.e. in Annelids, Arthropods and
Chordates)
• Superficial banding of the body
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Metamerism (segmentation)
Annelids
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Metamerism
(segmentation)
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•
Arthropods show external and internal segmentation, with clear
functional specialisation of body regions through tagmosis.
•
Chordates exhibit internal segmentation in structures like
vertebrae, somites, and spinal nerves, which facilitate coordinated
movement and structural support.
•
Segmentation may be homomeric segmentation in which the
segments are more or less the same, or heteromeric
segmentation wherein the segments differ from one another.
Cestoda
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3. Reproduction
Mario V Balzan Ph.D.
mario.balzan@mcast.edu.mt
1
Reproduction
• Type of reproduction: asexual and sexual. Parthenogenesis.
Adaptive meaning of the different reproductive patterns.
• DEVELOPMENT: Biological cycles. Larval and metamorphosis
development.
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Animal Reproduction
• Biological process by which living organisms generate new
individuals (offspring), to which they transmit their genetic
material.
• Sexual vs asexual reproduction.
• Asexual reproduction – there is only one parent; usually there are no
reproductive organs; gives rise to copies genetically identical to the
parent.
• Sexual reproduction – usually involves two parents. Germ cells
(gametes or sex cells) unite forming a zygote. The offspring is
genetically different from the parent. Creates multiple variations and
makes possible evolution of different forms.
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Asexual Reproduction
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Asexual Reproduction
• 1 parent
• Without reproductive organs
• Produces clones
• Found in bacteria and unicellular eukaryotes and in many
invertebrate phyla, such as cnidarians, bryozoans, annelids, and
echinoderms.
• Rare among vertebrates but animals of some taxa can reproduce
both asexually and sexually. In these groups, asexual reproduction
ensures rapid increase in numbers prior to the individual’s
attaining sexual maturity.
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Asexual Reproduction
• Types of asexual reproduction
• Binary Fission
• Multiple Fission or schizogony
• Budding
• Gemmulation
• Fragmentation
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Asexual Reproduction
• Binary Fission: the body of the unicellular parent divides by
mitosis into two approximately equal parts, each of which grows
into an individual similar to the parent.
• Binary fission may be lengthwise, as in flagellate unicellular
eukaryotes, or transverse, as in ciliate unicellular eukaryotes.
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Asexual Reproduction
• Multiple Fission (or schizogony): the nucleus divides repeatedly
before division of the cytoplasm, producing many daughter cells
simultaneously.
• Spore formation, called sporogony, is a form of multiple fission
common among some parasitic unicellular eukaryotes, for
example, malarial parasites.
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Asexual Reproduction
• Budding is an unequal division of an organism. A new individual
arises as an outgrowth (bud) from its parent, develops organs like
those of the parent and then detaches itself.
• Budding occurs in several animal phyla and is especially
prominent in cnidarians
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Asexual Reproduction
• Gemmulation is the formation of a new individual from an
aggregation of cells surrounded by a resistant capsule, called a
gemmule.
• In many freshwater sponges, gemmules develop in the fall and
survive the winter in the dried or frozen body of the parent. In
spring, the enclosed cells become active, emerge from the
capsule, and grow into a new sponge.
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Asexual Reproduction
• Fragmentation: a multicellular animal breaks
into two or more parts, with each fragment
capable of becoming a complete individual.
• Many invertebrates, for example, most
anemones and many hydroids, can reproduce
asexually by simply breaking into two parts and
then regenerating the missing parts of the
fragments.
• Many echinoderms can regenerate lost parts,
but this is not the same as reproduction by
fragmentation.
13
Sexual Reproduction
• Sexual reproduction is the production of individuals from the
fusion of gametes.
• Includes bisexual (or biparental) reproduction as the most
common form, involving two separate individuals.
• Hermaphroditism is a less common form of sexual reproduction.
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Sexual Reproduction
• Bisexual reproduction is the production of offspring formed by
the union of gametes from two genetically different parents.
• Offspring genetically different from the parent.
• Dioecious vs Monoecious:
• Dioecious - Different sexes, male and female (e.g. nearly all vertebrates).
• Monoecious – animals having both male and female organs. These
animals are Hermaphrodites.
15
Sexual Reproduction
16
•
Meiosis
•
Haploid gamete cells
•
Fertilisation
•
99% of animals reproduce sexually at
some point in their lives. Why?
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Sexual Reproduction
•
Meiosis
•
Haploid gamete cells
•
Fertilisation
•
99% of animals reproduce sexually at
some point in their lives. Why?
•
17
18
Genetic Recombination: Diploid Zygote
with equal number of chromosomes
from each parent but is a unique
individual bearing a recombination of
parental characteristics. -> Adding new
genetic combinations to a population.
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19
Fertilisation or
Syngamy
•
Types of fertilisation
•
Internal fertilisation:
•
•
•
20
Gametes inside the female
Aquatic or terrestrial environment
Frequent care of offspring
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Fertilisation or
Syngamy
•
Types of fertilisation
•
Internal fertilisation:
•
•
•
•
Gametes inside the female
Aquatic or terrestrial environment
Frequent care of offspring
External Fertilisation
•
•
•
•
Gametes released into the
environment
Generally aquatic environment
No offspring care
Production of many eggs.
Sponges (Porifera)
21
Hermaphroditism
•
Animals with sexual organs (testes and
ovaries) in the same individual.
Monoecious individuals.
•
Some fertilise themselves but most
avoid self-fertilisation.
•
Simultaneous Hermaphrodites:
•
Sequential Hermaphrodites
•
•
22
Maturation of gonads at the same time.
Maturation of gonads at different
times.
Coral (Cnidaria) spawning
Giant Clam (Tridacna
gigas; Mollusca)
spawning
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Reproductive Patterns
• Oviparous (“egg-birth”) – animals that lay their eggs outside the body
for development. Include the majority of vertebrates. Many abandon
their eggs indiscriminately while other display great care in finding
places that provide food for young when they hatch.
• Many invertebrates and some vertebrates such as amphibians, some fish, reptiles and
birds
• Ovoviviparous (“egg-live-birth”) – animals that incubate their eggs
internally, with embryos deriving nourishment from the egg yolk.
• Annelids, brachiopods, insects and gastropod molluscs and common in fish and reptiles
• Viviparous (“live-birth”) – fertilised eggs develop in the oviduct or
uterus with embryos deriving all their nourishment directly from the
mother.
• Mammals, some elasmobranchs, some amphibians, reptiles and invertebrates such as
scorpions, amphibians, reptiles and invertebrates such as scorpions
23
Parthenogenesis
• The development of an embryo from an unfertilized egg or one in which the
male and female nuclei fail to unite following fertilization.
• Ameiotic or Diploid Parthenogenesis:
• No meiosis occurs and the egg is formed by cell division.
• The offspring is therefore a clone of the parent.
• Some flatworms, rotifers, crustaceans, and insects.
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Parthenogenesis
25
Parthenogenesis
• The development of an embryo from an unfertilized egg or one
in which the male and female nuclei fail to unite following
fertilization.
• Ameiotic or Diploid Parthenogenesis:
• No meiosis occurs and the egg is formed by cell division.
• The offspring is therefore a clone of the parent.
• Some flatworms, rotifers, crustaceans, and insects.
• Meiotic Parthenogenesis
• The egg is formed by meiosis.
• The haploid begins development spontaneously and may or may not
be activated by the influence of sperm.
• Diploid condition may be restored by chromosomal duplication or by
autogamy (rejoining of haploid nuclei).
• Some flatworms, rotifers, annelids, mites, and insects.
• Case of bees, wasps and ants. Example: Honebees: Fertilised eggs > diploid females (workers, queen); unfertilised eggs -> meiotic
parthenogenesis -> haploid males (drones)
• Haplodiploidy - males are haploid; females are diploid.
26
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Animal Development
Animals having tissue organisation.
27
ORGANOGENESIS
FERTILISATION
EMERGENCE
OF THE
MESODERM
SEGMENTATION
Blastocoel
GASTRULATION
(2 germ layers)
MORULA
BLASTULA
28
Archenteron (primitive gut)
Blastopore
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29
1. Radial Holoblastic Cleavage
A. Sea Star (Isolectihal Egg):
• Isolectihal eggs have small, evenly distributed yolk.
• Cleavage is radial and holoblastic, meaning the entire egg divides
symmetrically.
• Results in uniform, symmetrical blastomeres.
B. Frog (Mesolecithal Egg):
• Mesolecithal eggs have moderate yolk concentrated at the vegetal pole.
• Cleavage is holoblastic, but slower at the vegetal pole due to yolk.
• Formation of the grey crescent, a region critical for dorsal-ventral axis
formation.
2. Spiral Holoblastic Cleavage
C. Nemertean Worm (Isolectihal Egg):
• Spiral cleavage occurs in spiralians (e.g., annelids, molluscs).
• Cells divide in a spiral pattern, leading to a helical arrangement.
• Typically found in organisms with isolectihal eggs.
3. Discoidal Meroblastic Cleavage
D. Chick (Telolecithal Egg):
• Telolecithal eggs have large amounts of yolk, mostly at the vegetal pole.
• Cleavage is meroblastic (partial), occurring only in the small, yolk-free area
(blastodisc).
• Common in birds and reptiles, where yolk hinders complete division.
4. Rotational Holoblastic Cleavage
E. Mouse (Isolectihal Egg):
• In mammals, cleavage is rotational and holoblastic.
• Initial divisions are perpendicular, followed by asynchronous divisions.
• Leads to formation of a morula and later a blastocyst, essential for
implantation.
30
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31
32
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33
34
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35
36
Feature
Protostomes
Deuterostomes
Cleavage
Pattern
Spiral,
determinate
Radial,
indeterminate
Blastopore Fate
Becomes the
mouth
Becomes the
anus
Coelom
Formation
Schizocoely Coelom forms
by splitting of
the mesoderm
Enterocoely –
Coelom forms
by outpocketing
of the
archenteron
Nervous
System
Ventral nerve
cord
Dorsal nerve
cord
Examples
Mollusks,
arthropods,
annelids
Chordates,
echinoderms,
hemichordates
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37
Coelom
• The coelom is a fluid-filled cavity within the
mesoderm.
• A space bounded by the mesoderm, where
organs are suspended by mesenteries.
• Allows for a more stable arrangement of
organs.
• Functions as an efficient hydrostatic skeleton,
facilitating movement through antagonistic
circular and longitudinal muscles.
• Mesenteries: provide an ideal site for blood
vessel networks, enhancing circulation.
• Support a more muscular gastrointestinal
tract, improving digestive efficiency.
• Enable the development of larger and more
complex body forms.
38
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Germ Layer
Structures
Endoderm
- Epithelium lining the digestive tract (except the oral cavity and anal canal) and the epithelium of its glands.
- Epithelium lining the urinary bladder, bile ducts, and liver.
- Epithelium lining the pharynx, Eustachian tube, tonsils, tympanic cavity, larynx, trachea, bronchi, and lungs.
- Epithelium of the thyroid, parathyroid, pancreas, and thymus glands.
- Epithelium lining the prostate, Cowper's glands, vagina, vestibule, urethra, and associated glands.
Mesoderm
- All cardiac and skeletal muscle tissue, and most of the smooth muscle tissue.
- Cartilage, bone, and other connective tissues.
- Blood, red bone marrow, and lymphatic tissue.
- Blood vessels and lymphatic vessels.
- Dermis of the skin.
- Fibrous tunic and vascular tunic of the eye.
- Mesothelium of the thoracic, abdominal, and pelvic cavities.
- Kidneys and ureters.
- Adrenal cortex.
- Gonads and genital ducts (excluding germ cells).
- Dura mater (outer layer of the meninges).
Ectoderm
- All nervous tissue.
- Epidermis of the skin.
- Hair follicles, arrector pili muscles, nails, and the epithelium of cutaneous (sebaceous and sweat) glands and mammary glands.
- Lens and cornea.
- Inner ear.
- Neuroepithelium of sensory organs.
- Epithelium of the oral and nasal cavities, paranasal sinuses, salivary glands, and parts of the anal canal.
- Epithelium of the pineal gland, pituitary gland, and adrenal medulla.
- Melanocytes (pigment-producing cells).
- Nearly all components of the skull and connective tissues of the head.
- Arachnoid and pia mater (meningeal layers).
39
Life Cycles
• Postembryonic development - a part of ontogeny that follows
embryonic development and ends with sexual maturation:
• Indirect Development
• Direct Development
40
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Indirect Development
Presence of free larval stage
(usually swimming).
More or less accentuated
metamorphosis to reach the adult
stage.
Aquatic and insect organisms.
41
Metamorphosis
It is the passage from larva to juvenile or
preadult. This is a crucial and dangerous
time in the animal's life. The animal
changes its habitat and lifestyle.
E.g. Free-swimming larvae -> Benthic
juveniles
It responds to environmental stimuli to
establish itself:
•
Negative phototropism.
•
Positive geotropism (towards gravity) ->
sinking to the bottom.
By physical, chemical and biological
stimuli, it detects suitable habitat
to establish itself
42
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43
Direct Development
• Copulation and internal fertilization (except in certain directdeveloping amphibians, fish, and insects).
• No free larval stage - juveniles resemble adults at birth or
hatching.
• Development occurs within the egg (incubation) or inside the
mother (gestation). In some insects (e.g., silverfish), juveniles
hatch as miniature versions of adults and continue moulting
throughout life.
• Parental care may or may not be present, depending on the
species. Many vertebrates exhibit parental care, whereas most
direct-developing insects do not.
44
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Direct Development
Female
Gametes
Copulation
Internal Fertilisation
Embryo incubated or
encapsulated
Adult
Birth or
hatching
Maturation
Juvenile
45
Topic 4. Protozoa
Mario V Balzan Ph.D.
mario.balzan@mcast.edu.mt
Protozoa
• The concept of Protozoa. Shape and function. Representative
types. Main parasitic groups.
Protozoa
•
Protozoa are: eurkaryotes, unicellular
and heterotrophs.
•
A paraphyletic group
•
•
•
•
Protozoa are paraphyletic due to their
diverse evolutionary origins, as they do
not form a single monophyletic
group.
Instead, they are spread across multiple
eukaryotic supergroups shown in the
figure, including Amoebozoa
(Entamoebae), Excavata (Diplomonads,
Trichomonads), and Alveolata (Ciliates,
Flagellates).
This classification excludes related
multicellular descendants, such as
animals, fungi, and plants, which share
common ancestors with certain
protozoan lineages.
Not a taxon, but a ‘level of evolution’
(protoplasmic level as opposed to the
cellular and tissue level of Metazoa).
Animal Concept
A polyphyletic group consist of organisms that are grouped together based on similar traits but do not share a recent common ancestor.
Fundamental differences between Protists
and Animals
Protists
Animals
• Protists:
• Animals:
• One type of somatic cell.
• Unicellular (though colonies,
syncytia, or multicellular stages
in life cycles exist) and usually
microscopic.
• Heterotrophic and/or
photoautotrophic.
• No embryonic development,
• No embryonic layers.
• Somatic differentiation into
tissues.
• Multicellular (differentiated
tissues and organs) and usually
macroscopic.
• Heterotrophic (though some
have zooxanthellae symbiosis).
• Embryonic development with
embryonic layers.
Trypanosoma
Amoeba
Foraminifera
Protozoa: General
Characteristics
• Protozoa are essentially
unicellular eukaryotic organisms
(some colonial or with
multicellular stages in their life
cycles), mostly microscopic,
without a cell wall, with at least
one motile stage in their life
cycle, and primarily
heterotrophic.
• They possess one or multiple
nuclei (e.g., macro- and
micronucleus in ciliates).
• They lack differentiated organs
or tissues but have specialized
intracellular organelles
(intracellular specialization).
Protozoa: General Characteristics
Size: They are microscopic, although some (e.g., foraminiferans) can be
visible to the naked eye.
Lifecycle and Distribution
• They exhibit diverse life cycles: free-living, symbiotic (mutualism,
commensalism, or parasitism). Over 10,000 symbiotic species
exist.
• They inhabit aquatic, terrestrial, or symbiotic environments.
• As a group, protozoa are eurytopic (broad ecological tolerance),
but as individual species, they tend to be stenotopic (narrow
ecological tolerance).
• Protozoa are important bioindicators.
Locomotion
• Some protozoa are sessile. Others move using cilia, flagella,
pseudopodia, or direct cellular movement.
• Pseudopodia are formed by cytoplasm (ectoplasm or ectoplasm
and endoplasm).
Locomotion
• Cilia and flagella - Cilia and flagella are composed of
microtubules arranged in a 9+2 pattern.
• Flagellates use flagella, ciliates travel via a ciliated body surface.
They are primarily involved in locomotion, but they can also
function in feeding, sensation, and other processes. Despite their
differences in length and movement patterns, cilia and flagella
share a similar internal structure known as the axoneme.
• Cilia usually shorter and occur together in larger numbers than
flagella which are usually solitary.
Locomotion
Eukaryotic flagellum. 1axoneme, 2-cell membrane, 3IFT (intraflagellar transport), 4basal body, 5-cross section of
flagellum, 6-triplets of
microtubules of basal body.
Locomotion
• Pseudopodia – temporary,
flexible extensions of the cell
membrane and cytoplasm used
for locomotion and feeding.
Figure: Arrows indicate the direction of a streaming protoplasm. First sign of a new pseudopodium is thickening of the
ectoplasm to form a clear hyaline cap, into which the endoplasm flows. As the endoplasm reaches the forward tip, it
fountains out and is converted into ectoplasm, forming a stiff outer tube that lengthens as the forward flow continues.
Posteriorly the ectoplasm is converted into fluid endoplasm, replenishing the flow. Substratum is necessary for amoeboid
movement.
Skeleton
• Most protozoa lack a
skeleton.
• Some have a simple
endoskeleton or an
exoskeleton.
• Many can form cysts in
response to adverse
conditions (resistance
mechanism in
changing
environments).
Nutrition
• Autotrophic: Through photosynthesis.
• Heterotrophic:
• Phagotrophic feeding: Ingestion of large food particles via
phagocytosis.
• Saprozoic feeding: Uptake of dissolved substances through pinocytosis
or diffusion.
Excretion
• Excretion occurs via diffusion,
with ammonia as the main
nitrogenous waste.
• Osmoregulation is carried out
by contractile vacuoles.
Reproduction
• Budding
• Binary fission
• Multiple fission
Reproduction
• Budding
• Binary fission
• Multiple fission
In Ciliates:
Reproduction
• Budding
• Binary fission
• Multiple fission – the body
divides into numerous daughter
individuals, often with residual
cytoplasmic masses. E.g. in
foraminifera, radiolaria and
sporozoan groups like
Plasmodium.
Sexual Reproduction
• Types of meiosis:
• Gametic meiosis: Occurs
during or just before gamete
formation, resulting in a
diploid cycle (e.g., Ciliates:
Paramecium).
Sexual Reproduction
• Types of meiosis:
• Zygotic meiosis: Occurs after fertilization, resulting in a haploid cycle
(e.g., Apicomplexa: Plasmodium), often with asexual reproductive
phases.
Sexual Reproduction
• Types of meiosis:
• Intermediate meiosis: Produces a diplo-haploid cycle (e.g.,
Foraminifera).
Sexual Reproduction - Fertilisation
• Autogamy: Fusion of gametic
nuclei within the same organism.
• Conjugation: Exchange of genetic
material between two individuals
without cell fusion.
• Syngamy: Fertilization between
two gametes (isogamy and
anisogamy).
Diversity
Diversity
• Free-living organisms, many endosymbionts of the
digestive tract of vertebrates and invertebrates,
and parasites.
• Flagellates
• Organisms without mitochondria, with organelles
adapted to low-oxygen conditions.
Diversity
• Main groups:
• Excavata: Includes flagellates like Giardia (intestinal parasite),
Trichomonas (urogenital infections), and Trypanosoma (causing
sleeping sickness).
• Amoebozoa: Includes amoeboid protozoa such as Entamoeba
(dysentery-causing parasite).
• Alveolata: Includes:
• Dinoflagellates (some photosynthetic, some bioluminescent, some toxic
blooms).
• Apicomplexans (intracellular parasites like Plasmodium, the malaria parasite).
• Ciliates (complex eukaryotes with cilia, e.g., Paramecium, Balantidium coli).
Diversity
Excavata: Metamonadales
Diplomonadids
Giardia duodenalis is a protozoan
flagellate (Diplomonadida).
Diversity
Excavata: Metamonadales
Parabasalids
Trichomonas (in vagina, mouth,
esophagus, etc., of humans, cattle,
chickens, etc.)
Diversity
Excavata: Metamonadales
Parabasalids
Trichomonas (in vagina, mouth,
esophagus, etc., of humans, cattle,
chickens, etc.)
Diversity
Excavata: Metamonadales
Retortamonada
•
Commensals (live inside hosts
without causing harm)
•
Do not have mitochondria or a Golgi
apparatus
•
Well-developed cytostome
Diversity
Excavata: Discoba, Euglenozoa
Morphotypes
Diversity
Excavata: Discoba, Euglenozoa
• Leishmania (in the liver, spleen, etc., of mammals)
Diversity
Excavata: Discoba, Euglenozoa
• Trypanosoma (in the blood of fish, amphibians, reptiles, birds, and
mammals)
Diversity
Excavata: Discoba, Heterolobosea
Primary Amoebic Meningoencephalitis (PAM)
Diversity
Amoebozoa
• Amoebas – NOT a monophyletic group if Rhizaria and others are
included)
• Locomotion by lobopodian.
Diversity
Amoebozoa
• Amoebas – NOT a monophyletic group if Rhizaria and others are
included)
• Locomotion by pseudopodia.
Pseudopodia – temporary, flexible
extensions of the cell membrane
and cytoplasm used for
locomotion and feeding.
Diversity
Amoebozoa
Amoebic dysentery (severe intestinal disturbances)
Entamoeba sp.
Figure: Entamoeba histolytica / dispar cysts stained with iodine from an infected olive
baboon, Papio anubis. The cysts of Entamoeba histolytica and Entamoeba ​dispar are
considered morphologically indistinguishable. Mature cysts are spherical, have 4
nucleii, and measure 12 to 18 µm in diameter.
Diversity
Amoebozoa
Diversity
Amoebozoa
Free-living, commensal or parasitic.
Diversity
Alveolata. Principal groups;
Dinoflagellates
Apicomplexa
Ciliates
Diversity
Alveolata: ApicomplexaAlveolata: Apicomplexa
Class: Coccidia
Genera: Toxoplasma, Eimeria
• Intracellular parasites
• Presence of an apical complex
• No cilia or flagella (except for some microgametes in certain
groups)
• Internal membrane complex
• Form cysts
• Lifecycle include both sexual (gamogony) and asexual
(schizogony) reproduction, such as in malaria parasites
(Plasmodium)
Alveolata: Apicomplexa
Class: Coccidia
Genera: Plasmodium,
Toxoplasma, Eimeria
Alveolata: Apicomplexa
Class: Coccidia
Eimeria
The life cycle of a typical Eimeria species.
Sporozoites (A) excyst from sporocysts in the
intestinal tract of Gallus gallus domesticus.
Sporozoites infect a host intestinal epithelial
cell and initiate merogony (B) to produce
mature meronts (= schizonts). Merozoites exit
and infect neighboring host intestinal
epithelial cells for a genetically determined
number of merogonic cycles (C–D). After
these merogonic cycles, merozoites initiate
gametogony (E) to produce macrogametes (F)
and microgametes that mature within a
microgamont (= microgametocyte; G). Motile
microgametes (H) locate and fertilize a
mature macrogamete producing a zygote. The
zygote is shed in the feces as an unsporulated
oocyst (I). Sporogony (I–L) occurs in the
environment to produce a sporulated,
infective oocyst (L) that contains 4
sporocysts, each containing 2 infective
sporozoites (from Barta [2]; used with
permission).
https://www.sciencedirect.com/science/artic
le/pii/S1056617119306622#fig1
Alveolata: Apicomplexa
Class: Coccidia
Toxoplasma
Toxoplasma gondii is a protozoan
parasite that infects most species of
warm-blooded animals, including
humans, and causes the disease
toxoplasmosis.
https://www.cdc.gov/dpdx/toxoplasmosi
s/index.html
Alveolata: Apicomplexa
Class: Aconoidasida
Plasmodium (malaria)
Alveolata:
Ciliates
•
Have cilia, some are sessile.
•
Possess two types of nuclei:
macronucleus and
micronucleus:
•
•
Macronucleus –
Controls everyday
cellular functions
(transcriptionally
active).
Micronucleus –
Functions as the
germline nucleus
(transcriptionally silent
but undergoes meiosis)
•
Asexual reproduction by
binary fission, budding, and
multiple fission or sexual
reproduction by conjugation
and syngamy.
•
Generally free-living, but
some are commensal or
parasitic.
•
A highly diverse and complex
group with specialized
organelles.
Spirostomum minus
Alveolata: Ciliates
Ciliates (e.g. Paramecium) move using cilia, which are short,
hair-like structures covering their surface. Their movement
is based on coordinated ciliary beating, which generates
fluid flow and propels the organism through its environment.
Alveolata: Ciliates
Conjugation
Conjugation is initiated when two
compatible mating types come into
contact and adhere via their oral grooves.
Alveolata: Ciliates
• Paramecium, Vorticella (in Penaeus)
Alveolata: Ciliates
• Trichodina (on fish gills), Cryptocaryon, Ichthyophthirius (white
spot disease in fish)
Alveolata: Ciliates
• Trichodina (on fish gills), Cryptocaryon, Ichthyophthirius (white
spot disease in fish)
Alveolata: Ciliates
• Balantidium spp.
• Balantidium (=Neobalantidiu
m) (=Balantioides) coli, a large
ciliated protozoan, is the only
ciliate known to be capable of
infecting humans. It is often
associated with swine, the
primary reservoir host.
Diversity
Topic 5 - Porifera and
Cnidaria
Mario V Balzan Ph.D.
mario.balzan@mcast.edu.mt
Topic 5 - Porifera and Cnidaria
• 5. PORIFERA. Cellular elements and structural
types. CNIDARIA. Basic organization. Biological cycles
Porifera
• General
Characteristics:
• Multicellular, but
phylogenetically
independent from
other metazoans
(Parazoans).
• Embryonic layers
are not
homologous to
metazoans. No
true tissues.
General
Characteristics
• Heterotrophic multicellular
animals.
• Body formed by an aggregate of
differentiated cells.
• No symmetry or radial
symmetry.
• Aquatic animals, mostly marine.
• Benthic, sessile (fixed to the
substrate), filter feeders (adults).
• Highly variable sizes and shapes
(up to 2 metres!).
General Characteristics
• Canal system: Internal canal
system and surface openings
"pores" (ostioles) through which
water circulates for oxygen and
food exchange.
• Osculum
General Characteristics
• Cellular aggregation
• Sponge = Epithelum + Mesanchyma
• Epithelial cells (Pinacoderm – the outer
protective layer):
• Pinacocytes: Flat cells forming the outer
surface, controlling water flow by
contracting.
• Porocytes: Tube-like cells forming pores
(ostia) that allow water entry.
• Myocytes: Contractile cells regulating the
opening/closing of pores.
• Choanocytes (Choanoderm): also called
“coral cells”. They create water currents and
capture food particles. They line the inner
chamber of the sponge.
• Mesenchymal cells (Mesohyl): inner
jelly-like matrix with various cell types.
General Characteristics
• Cellular aggregation
• Sponge = Epithelum +
Mesanchyma
• Epithelial cells (Pinacoderm – the
outer protective layer):
• Mesenchymal cells (Mesohyl):
inner jelly-like matrix with various
cell types.
• Amoebocytes and Archaeocytes
(sclerocytes, spongocytes,
archaeocytes, collencytes) (Mesohyl)
General Characteristics
Canal system and water movement
1. Asconoid (Simplest Type): Small, tube-shaped sponges (e.g., Leucosolenia, Clathrina).
• Water enters via dermal pores → Spongocoel (lined by choanocytes) → Exits via a single Osculum.
• Limited food capture due to dead space in large cavities.
• Only found in Class Calcispongiae.
2. Syconoid (Intermediate Complexity)
• Larger than asconoids with a folded body wall forming choanocyte-lined canals.
• Water enters via dermal ostia → Incurrent canals → Prosopyles → Radial canals → Spongocoel → Exits
via Osculum.
• Increased surface area for food capture.
• Found in Class Calcispongiae and some Hexactinellida.
3. Leuconoid (Most Complex & Efficient)
• Largest sponges with branched canal systems (e.g., Euspongia).
• Water moves through a network of incurrent canals → flagellated chambers (lined with choanocytes)
→ excurrent canals → exits via multiple oscula.
• Maximises food collection and sponge size.
• Common in Demospongiae (largest sponge class).
Skeletal Structures
• Crystalline spicules, calcareous (aragonite or calcite) or siliceous
(silicon hydroxide) spicules
• Protein-based skeleton (spongin)
Reproduction
• Asexual Reproduction
• Fragmentation: High regenerative capacity.
• External Budding: Formation of external buds, a mechanism for colony
formation.
• Gemmulation: Formation of internal buds, a mechanism for resistance
and dispersion.
Section through a gemmule of a freshwater sponge (Spongillidae). Gemmules are a mechanism for
survival of the harsh conditions of winter. On return of favorable conditions, the archaeocytes exit
through the micropyle to form a new sponge. The archaeocytes of the gemmule give rise to all the cell
types of the new sponge structure.
• Sexual Reproduction
Reproduction
• Mostly monoecious.
• Cross-fertilisation: Internal or external.
• Gametes derived from choanocytes or archaeocytes.
• Post-embryonic development: Indirect.
Classification
Classification
• Calcarea
• All 3 types of body
organisation;
• Composition of
Spicules: Calcium
Carbonate (CaCO3);
• Number of Rays: 3-4 or
needle shaped;
• Location: Marine
Environment (shallow
environments,
attached to rocks and
substrates).
• Example: Leucosolenia
sp.
Classification
• Calcarea
• All 3 types of body
organisation;
• Composition of
Spicules: Calcium
Carbonate (CaCO3);
• Number of Rays: 3-4
or needle shaped;
• Location: Marine
Environment (shallow
environments,
attached to rocks and
substrates).
Hexactinellida
• Glass sponges
• Composition of Spicules:
Siliceous
• Number of Rays: 6
• Syconoid or Leuconoid
structure
• Location: Marine Environment,
found in deep water.
• Example: Euplectella sp.
(Venus’ flower basket).
Demospongiae
• Siliceous spicules not sixrayed and/or spongin fibres.
• All Leuconoid.
• Only one freshwater family,
the rest are marine.
• 95% of known species.
• Example: Spongia officinalis
Cnidaria
CNIDARIA. Basic organization. Biological cycles
Cnidaria
• Diploblastic: Two germ layers (ectoderm and endoderm).
Cnidaria
Mesoglea
(Derived from the
ectoderm)
• Body wall consists of two tissues: epidermis and gastrodermis,
with mesoglea in between.
Cnidaria
• Primary radial
symmetry
• Dimorphism:
• Sessile forms =
polyps
• Pelagic forms =
medusae
Cnidaria
• Nerve net system: No defined ganglionic centres.
• Primitive muscle cells (derived from ectoderm and endoderm).
• Gastrovascular cavity: Functions in circulation, digestion, gas exchange,
and excretion.
• No circulatory system, excretory organs and specialised respiratory
organs.
Cnidaria
• Possess Cnidocytes, making them unique among
metazoans. Cnidocytes are abundant in the oral region
and tentacles, reflecting their role in feeding and defence.
• Cnidocytes contain nematocysts, which are organelles
that can deliver a sting or toxin to prey or predators.
Several types of
nematocysts shown after
discharge. At bottom are
two views of a type that
does not impale the prey,
rather it recoils like a
spring, catching any
small part of the prey in
the path of the recoiling
thread.
Cnidaria
• Movement:
• Epitheliomuscular cells + Hydrostatic skeleton (gastrovascular cavity).
• May have skeletons of chitin or calcium carbonate.
Cnidaria
These hydrozoans form calcareous skeletons that resemble true coral. A, Stylaster roseus (order Stylasterina) occurs commonly in
caves and crevices in coral reefs. These fragile colonies branch in only a single plane and may be white, pink, purple, red, or red with
white tips. B, Species of Millepora (order Milleporina) form branching or platelike colonies and often grow over the horny skeleton of
gorgonians, as is shown here. They have a generous supply of powerful nematocysts that produce a burning sensation on human skin,
justly earning the common name fire coral.
Cnidaria
• Feeding:
• Predators.
• Digestive cavity (gastrocoel): One opening (mouth).
• Extracellular digestion (glandular cells release enzymes) + Intracellular
digestion (phagocytosis or pinocytosis, with digestive vacuoles).
Generalized life cycle of a cnidarian.
Reproduction
• Metagenetic cycle:
• Polyp phase: Asexual reproduction.
• Medusa phase: Sexual reproduction.
• Some groups lack one of these stages.
• Sexual phase (medusa):
• Dioecious.
• Gonads produce gametes (meiotic
gametogenesis).
• External or internal fertilisation.
• Free-swimming planula larva.
• Asexual phase (polyp):
• Budding/strobilation.
• Can form colonies.
• Gonozoids/Gastrozoids.
Lifecycle of Obelia sp.
Cnidaria - Classification
Cnidaria - Classification
HYDROZOANS:
Marine and freshwater.
Solitary and colonial
forms.
Polyp stage predominates
(although one stage may
be absent).
E.g.: Obelia sp., Hydra sp.,
Physalia physalis
(Portuguese man-of-war).
SCYPHOZOANS:
Medusa stage dominates;
polyp stage reduced or
absent. Almost always
solitary. Mostly dioecious.
E.g.: Aurelia aurita (moon
jellyfish), Pelagia noctiluca
(mauve stinger).
CUBOZOANS:
Box jellyfish with cubeshaped medusae. Welldeveloped eyes. Strong
swimmers and highly
venomous.
E.g.: Chironex fleckeri (sea
wasp), Carukia barnesi
(Irukandji jellyfish).
ANTHOZOANS:
Only polyp stage. Octamerous
(8 tentacles) or hexamerous
(multiples of 6 tentacles)
structures. Includes
anemones, corals, and sea
fans. Marine, found at all
depths. Solitary and colonial.
E.g.: Actinia equina (beadlet
anemone), Corallium rubrum
(red coral).
Topic 6 - Platyhelminthes
Mario V Balzan Ph.D.
mario.balzan@mcast.edu.mt
• 6. PLATYHELMINTHES. Basic organization of Turbellaria,
Trematoda and Cestoda. Morphological particularities and
biological cycles of parasitic platyhelminthes.
Platyhelminthes
• Triploblastic and aceolomate metazoans
Platyhelminthes
• Triploblastic metazoans
Platyhelminthes
• Protostomes
• Bilateral Symmetry
• Definite polarity of anterior and posterior ends; body flattened
dorsoventrally
Platyhelminthes
• Nervous system composed of
cerebral ganglia and a ventral
nerve cord.
• General characteristics:
• Generally dorsoventrally
flattened. Vermiform in free-living
species, with a head carrying
sensory organs.
• Found in marine, freshwater, and
terrestrial (humid) environments.
Many are parasitic
Platyhelminthes
• Nervous system composed of
cerebral ganglia and a ventral
nerve cord.
• General characteristics:
• Generally dorsoventrally
flattened. Vermiform in free-living
species, with a head carrying
sensory organs.
• Found in marine, freshwater, and
terrestrial (humid) environments.
Many are parasitic
Platyhelminthes
• Feeding: Almost exclusively on other
animals. Some feed on algae, others
are carnivorous, but the majority are
parasites.
• Parasitism implies:
• Presence of specialized attachment
organs for adhering to the host.
• Modification of the external surface.
• Reduction or elimination of the intestine.
• Expansion of the reproductive system.
• Tegument: Syncytial vs. Ciliated
cellular epidermis
• Parasitic groups: Microvilli, folds,
channels, spines
• Free-living forms
Platyhelminthes
• Digestive System:
• Generally including a mouth, a
pharynx, and an intestine. Absent in
some parasites.
• Digestion in 2 stages: Extracellular +
intracellular digestion.
• Extracellular digestion: Enzymes break
down food in the gastrovascular cavity.
• Intracellular digestion: Nutrients are
further digested within individual cells
after absorption.
Platyhelminthes
• Gas Exchange
• By diffusion. No circulatory system.
• Absorptive and secretory tegument.
Platyhelminthes
• Excretory System:
lack of internal opening
• Protonephridia as excretory organs (since they have an anus).
Platyhelminthes
• Reproduction
• Asexual reproduction (fission) – regeneration (the body splits into 2)
Platyhelminthes
• Reproduction
• Asexual reproduction (fission) – regeneration (the body splits into 2)
• Most are hermaphrodytes (monoecious) but practice cross-fertilisation.
Sexual Reproduction
Platyhelminthes - Classification
Platyhelminthes - Classification
• Turbellarians (free-living):
Freshwater, humid, and
marine habitats.
• Broad and oval body
• Poorly differentiated head but
with eye spots and
auricles/tentacles
• Ventral mouth at mid-body
• Eversible pharynx
Prostheceraeus roseus
Dugesia subtentaculata
Platyhelminthes - Classification
• Monogeneans (single-host
parasites):
• Ectoparasites of fish (amphibians,
reptiles, marine mammals).
• Morphologically:
• Anterior: Mouth, buccal suckers
• Posterior: Haptor (suckers, hooks,
clamps, etc.)
• Direct life cycle
• Transmission pathways:
• Open environment: Eggs →
Oncomiracidium
• Cultures: Eggs → Oncomiracidium
Pseudothoracocotyla
ovalis (Polyopisthocotylea)
from the gills of the Spanish
Macherel Scomberomorus
commerson on the Great
Barrier Reef. Note the
opisthaptor bearing a large
number of clamps, and
posterior large and small
hooks. Female reproductive
system except vitellarium red.
Platyhelminthes - Classification
• Monogeneans (single-host
parasites):
• Ectoparasites of fish (amphibians,
reptiles, marine mammals).
• Morphologically:
• Anterior: Mouth, buccal suckers
• Posterior: Haptor (suckers, hooks,
clamps, etc.)
• Direct life cycle
• Transmission pathways:
• Open environment: Eggs →
Oncomiracidium
• Cultures: Eggs → Oncomiracidium
Sparicotyle chrysophrii is a species of monogenean,
parasitic on the gills of the marine fish. It belongs to the
family Microcotylidae. Its type-host is the gilt-head
seabream (Sparus aurata). Causes high mortality in fish
cages.
Platyhelminthes - Classification
• Trematodes: Digeneans
• Endoparasites (many cause diseases in humans
and domestic animals).
• May have attachment organs (around the mouth
and ventrally): suckers
• Complex life cycle: 1 to 3 intermediate hosts
(asexual reproduction) and a definitive host
(usually a vertebrate) (sexual reproduction).
• Example Species: Clonorchis sinensis (Human
liver fluke, found in raw fish); Fasciola hepatica
(Liver fluke of sheep and ruminants).
Platyhelminthes - Classification
• Trematodes: Digeneans
• Endoparasites (many cause diseases in humans
and domestic animals).
• May have attachment organs (around the mouth
and ventrally): suckers
• Complex life cycle: 1 to 3 intermediate hosts
(asexual reproduction) and a definitive host
(usually a vertebrate) (sexual reproduction).
• Example Species: Clonorchis sinensis (Human
liver fluke, found in raw fish); Fasciola hepatica
(Liver fluke of sheep and ruminants).
Platyhelminthes - Classification
• Trematodes:
Digeneans
Platyhelminthes - Classification
• Trematodes:
Digeneans
Platyhelminthes - Classification
• Cestodes
• Endoparasites of vertebrate intestines (rarely in invertebrates).
• Lacking mouth and digestive tract, absorb digested food directly through
their microvillous tegument.
• Well-developed muscular system (circular and longitudinal fibres).
• Long, flat bodies: Scolex + Strobila (series of proglottids).
• Examples:
• Taenia solium (Pork tapeworm)
• Taenia saginata (Beef tapeworm)
• Echinococcus granulosus (Hydatid cyst tapeworm)
• Juveniles in mammals (including humans), adults in canids.
• Cestodes
• Cestodes
Cystic
Echinococcosis
(Echinococcus
granulosus
sensu lato)
7. Molluscs
Mario V. Balzan Ph.D.
mario.balzan@mcast.edu.mt
• 7. MOLLUSCS. General characteristics. Gastropoda, Bivalvia
and Cephalopoda. Groups of veterinary interest
Molluscs
• Triploblastic metazoans
• Bilateral symmetry
• Protostomes
• General Characteristics
Molluscs
• Highly diverse group with a wide range of forms, sizes, and
colours.
• Over 93,000 living species and 70,000 fossil species, with an
estimated half yet to be described.
• Found in marine, freshwater, and terrestrial environments.
• Mostly free-living, but some are parasitic.
Molluscs
• Body Organisation
1. Head
2. Muscular Foot
3. Visceral Mass
4. Mantle
5. Mantle Cavity (Pallial Cavity)
6. Shell
Molluscs
• Head
• Marked cephalization (accumulation
of sensory and feeding structures).
• Variations exist depending on the
group.
• Mouth contains a radula (except in
bivalves).
Diagrammatic saggital view of the buccal cavity of a
gastropod, showing the radula and how it is used. The
rest of the body of the snail is shown in green. The food is
shown in blue. Muscles that control the radula are shown
in brown. The surface of the radular ribbon, with
numerous teeth, is shown as a zig-zag line
• Muscular Foot
Molluscs
• Ventral body extension.
• Highly adaptable: used for crawling, swimming, burrowing,
attachment, or propulsion.
Molluscs
• Visceral Mass
• Contains internal organs.
• Bordered ventrally by the foot and dorsally by the mantle.
• Mantle
• Dorsal body wall that surrounds the visceral mass.
• Forms one or two lobes that cover the body.
• Secretes the shell (if present).
Molluscs
• Mantle Cavity (Pallial Cavity)
• Space between the mantle and the body.
• Contains gills (ctenidia) for respiration.
• In pulmonates, it functions as a lung.
• Also, the site where digestive, excretory, and reproductive
products are expelled.
Molluscs
• Shell
• External calcium carbonate
exoskeleton.
• Secreted by shell glands in the
mantle.
• Highly variable in shape and size.
• Composed of three layers:
• Periostracum (outer protein
layer).
• Prismatic layer (calcium
carbonate prisms).
• Nacreous layer (inner,
continuously secreted layer
that thickens over time).
mothe pearl
Molluscs
• Shell
• External calcium carbonate
exoskeleton.
• Secreted by shell glands in the
mantle.
• Highly variable in shape and size.
• Composed of three layers:
• Periostracum (outer protein
layer).
• Prismatic layer (calcium
carbonate prisms).
• Nacreous layer (inner,
continuously secreted layer
that thickens over time).
Molluscs
• Digestive System
• Complete digestive tract with a mouth and anus.
• Large number of digestive glands.
Molluscs
• Circulatory System
• Open circulatory system (except cephalopods).
• Three-chambered heart (two atria and one ventricle).
• Circulatory fluid: Haemolymph.
• Reduced coelom, limited to the pericardial cavity.
Molluscs
• Gas Exchange
• Specialized respiratory organs:
• Gills (ctenidia) in the mantle cavity.
• Lungs in pulmonate molluscs (gas exchange occurs in
the mantle cavity wall).
Molluscs
• Excretory System
• Metanephridia:
• Paired tubular excretory organs (sometimes single).
• Filters coelomic fluid and expels waste into the mantle
cavity.
Molluscs
• Nervous System
• Two pairs of ganglia.
• Longitudinal nerve cords with transverse
commissures.
• Sensory organs:
• Tactile, olfactory, gustatory, equilibrium, and visual
structures.
Molluscs
• Reproductive System
• Mostly dioecious (separate sexes).
• Some hermaphrodites (sequential or
simultaneous).
• External or internal fertilization.
• Mainly oviparous, though some are
ovoviviparous.
• Development may be direct, mixed, or
indirect:
• Trochophore larva.
• Veliger larva (after the trochophore stage).
Molluscs - Classification
https://www.frontiersin.org/journals/ecology-andevolution/articles/10.3389/fevo.2024.1327007/full
Numbers along y-axis are millions of years before present (Ma).
Numbers at nodes represent the average age of the split.
https://www.nature.com/articles/s41598-019-56728-w
Molluscs - Classification
• Class Gastropoda
• Name derived from Gaster (stomach) + Poda (foot).
• Most diverse class with 70,000 living species and 15,000 fossil species.
• Includes terrestrial, freshwater, and marine species.
• Mostly herbivorous, but some are carnivorous.
• Oviparous, mostly with external fertilization.
Molluscs - Classification
• Torsion in Gastropods
• Torsion is the rotation of the
visceral mass, mantle, and shell
180˚ with respect to the head and
foot of the gastropod during larval
development. This rotation brings
the mantle cavity and the anus to
an anterior position above the
head.
• Pallial cavity and anus move from
posterior to anterior.
• Organs on the right-side shift to
the left.
• Digestive tube bends into a Ushape.
• Nerve cord takes on a figure-eight
shape.
Molluscs - Classification
• Diversity in Gastropods
• Prosobranchs (marine,
freshwater, and terrestrial
snails):
• Breathe using gills (anterior
position).
• Dioecious.
• Opisthobranchs (sea slugs, sea
hares):
• Breathe using gills (posterior
position).
• Monoecious.
Molluscs - Classification
• Pulmonates:
• Mostly terrestrial.
• Breathe using lungs.
• Monoecious.
• Some species have veterinary
importance (e.g., Lymnaea sp.).
Molluscs - Classification
• Class Bivalvia
• Includes mussels, oysters, and
clams.
• 20,000 living species, 15,000 fossil
species.
• Mostly marine.
• Laterally compressed body.
• No radula.
• Breathe using gills.
• Two-part shell (bivalve).
• Mostly dioecious, with external
fertilization.
• Oviparous.
Molluscs - Classification
• Class Cephalopoda
• Includes nautiluses, octopuses,
squids, and cuttlefish.
• 650 living species, 7,500 fossil
species.
Molluscs - Classification
• Body Reorganization in Cephalopods
• Foot modified into a siphon and tentacles
around the mouth.
• Highly variable shell structure:
• External shell (e.g., nautilus).
• Internal shell (e.g., cuttlefish, squid).
• No shell (e.g., octopuses).
External Shell
Internal Shell
No Shell
Cuttlefish bone
(made of calcium
carbonate and
serves a crucial
role in buoyancy
control; porous
and chambered)
Molluscs - Classification
• Body Reorganization in Cephalopods
• Foot modified into a siphon and tentacles
around the mouth.
• Highly variable shell structure:
• External shell (e.g., nautilus).
• Internal shell (e.g., cuttlefish, squid).
• No shell (e.g., octopuses).
SEM images of cuttlefish bone
Cuttlefish bone
(made of calcium
carbonate and
serves a crucial
role in buoyancy
control; porous
and chambered)
Molluscs - Classification
• Cephalopod Characteristics
• Exclusively marine.
• Gills for respiration.
• Highly developed nervous system and
sensory organs.
• Closed circulatory system (unlike other
molluscs).
• Carnivorous.
• Reproduction:
• External or internal fertilization.
Annelids
Introduction
• Most members of phylum Annelida are segmented worms living in marine, freshwater, and moist
terrestrial habitats.
• Marine bristle worms, leeches, and the familiar earthworms belong to this group. Annelida now
includes pogonophoran and vestimentiferan worms, formerly either placed together in phylum
Pogonophora, or placed in distinct phyla: Pogonophora and Vestimentifera. These deep-ocean worms
belong in clade Siboglinidae.
• Members of the former phylum Echiura are placed within Annelida. These sausage-shaped “spoon
worms” are not segmented but do contain repeated body parts that suggest a segmented ancestor.
• Worms formerly in phylum Sipuncula are benthic marine animals with unsegmented bodies, but
phylogenies using molecular sequence data place sipunculans within phylum Annelida as shown in the
following figure.
General characteristics
General characteristics
• Phylum Annelida largely consists of segmented worms. It is a diverse phylum, numbering
approximately 15,250 species, the most familiar of which are earthworms and freshwater worms
(oligochaetes) and leeches (class Hirudinida).
• However, approximately two-thirds of the phylum comprises marine worms (polychaetes), which
are less familiar to most people.
• Some polychaetes are grotesque in appearance,whereas others are graceful and beautiful.
• They include clamworms, plumed worms, parchment worms, scaleworms, lugworms, and many
others.
• The bodies of most annelids are divided into similar segments (also called metameres) arranged
in linear series and externally marked by circular rings called annuli (the name of the phylum
refers to this characteristic).
• Body segmentation (metamerism) is a division of the body into a series of units, each of which
contains similar components of all major organ systems. In annelids the segments are delimited
internally by septa.
General characteristics
• Annelids are sometimes called “bristle worms” because, with the exception of leeches, most
annelids bear tiny chitinous bristles called setae (L. seta, hair or bristle).
• Short, needlelike setae help anchor segments during locomotion and long, hairlike setae aid
aquatic forms in swimming.
• Since many annelids burrow or live in secreted tubes, stiff setae also aid in preventing the worm
from being pulled out or washed out of its home.
• Annelids have a worldwide distribution, and a few species are cosmopolitan.
• Polychaetes are chiefly marine forms. Most are benthic, but some are pelagic in the open seas.
• Oligochaetes and leeches occur predominantly in freshwater or terrestrial soils. Some freshwater
species burrow in mud and sand and others among submerged vegetation.
• Many leeches are predators, specialized for piercing their prey and feeding on blood or soft
tissues.
• A few leeches are marine, but most live in freshwater or in damp regions.
• Leeches typically have suckers at both ends of the body for attachment to the substratum or to
their prey.
Body plans
• The annelid body typically has a two-part head, composed of a prostomium and a peristomium,
followed by a segmented body and a terminal portion called the pygidium bearing an anus
(Figure 17.2).
• The head and pygidium are not considered to be segments.
• New segments differentiate during development just in front of the pygidium. Thus, the oldest
segments are at the anterior end and the youngest segments are at the posterior end.
• Each segment typically contains respiratory, nervous, and excretory structures, as well as a
coelom.
• Flaps called parapodia may be present on each segment.
• In most annelids the coelom develops embryonically as a split in the mesoderm on each side of
the gut (schizocoel), forming a pair of coelomic compartments in each segment.
• Peritoneum (a layer of mesodermal epithelium) lines the body wall of each compartment,
forming dorsal and ventral mesenteries that cover all organs (Figure 17.3).
• Peritonea of adjacent segments meet to form septa, which are perforated by the gut and
longitudinal blood vessels.
• The body wall surrounding the peritoneum and coelom contains strong circular and longitudinal
muscles adapted for swimming, crawling, and burrowing (Figure 17.3).
Body plans
• Except in leeches, the coelom of most annelids is filled with fluid and serves as a hydrostatic
skeleton as described in the opening essay.
• Crawling motions are produced by alternating waves of contraction by longitudinal and circular
muscles passing down the body (peristaltic contractions). Forces powerful enough for rapid
burrowing as well as locomotion can thus be generated.
• Swimming forms use undulatory rather than peristaltic movements in locomotion.
• An annelid body has a thin outer layer of nonchitinous cuticle surrounding the epidermis.
• Paired epidermal setae are ancestral for annelids, although they have been reduced or lost in
some.
• The annelid digestive system is not segmented: the gut runs the length of the body perforating
each septum.
• Longitudinal dorsal and ventral blood vessels follow the same path, as does the ventral nerve
cord.
• Historically, annelids were divided among three classes: Polychaeta, Oligochaeta, and Hirudinida.
Phylogenetic analyses show polychaetes and oligochaetes to be paraphyletic groups; leeches form
a clade. Leeches and former members of Oligochaeta form a clade called Clitellata, characterized
by presence of a reproductive structure called a clitellum. Oligochaetes arose within Polychaeta,
so the term “polychaete” is descriptive rather than taxonomic.
Body plans
• Polychaete is a term used to denote any of 80 morphologically distinct families of worms, typically
those with many setae. recent phylogenies based on molecular characters have supported two
main groups of annelids: Errantia and Sedentaria.
• The division of annelids into two such groups, one errant (freely moving; Figure 17.2) and the
other sedentary (spending most of their lives in tubes or burrows; Figure 17.4) was proposed long
ago on morphological grounds and later rejected. Recently these two groups have been
supported by phylogenies based on molecular characters. Sedentaria (Latin sedere, to sit)
contains some
• polychaetes, as well as oligochaetes and leeches (Clitellata; Figure 17.1). Most other polychaetes
are in Errantia (Latin errare, to wander).
• Many of these, like the clam worm, Nereis (Greek, name of a sea nymph), are predatory. They
have an eversible muscular pharynxarmed with jaws or teeth that can be thrust out with
surprising speed to capture prey (Figure 17.2A).
• Errantia and Sedentaria together form the new group Pleistoannelida.
• There are five groups of annelids placed outside Pleistoannelida; two of these excluded annelids
ae Sipuncula and Chaetopteridae.
Errantia
• Errantia comprises the motile polychaetes within Pleistoannelida.
• Most errant polychaetes (Gr. polys, many, + chaitē, long hair) are marine, and while most are 5 to
10 cm long, some are less than 1 mm, and others may be as long as 3 m.
• They may be brightly coloured in reds and greens, iridescent, or dull.
• Many polychaetes are euryhaline and can tolerate a wide range of environmental salinity.
• The freshwater polychaete fauna are more diversified in warmer regions than in temperate zones.
• Many polychaetes live under rocks, in coral crevices, or in abandoned shells. Some are planktonic.
• They play a significant part in marine food chains because they are eaten by fish, crustaceans,
hydroids, and many other predators.
• Polychaetes have a well-differentiated head with specialized sense organs; paired appendages,
called parapodia, on most segments; and no clitellum (see Figure 17.2).
• As their name implies, they have many setae, usually arranged in bundles on the parapodia.
• They exhibit the most pronounced specialization of sensory organs found in annelids.
Form and Function
• A polychaete typically has a prostomium, which may or may not be retractile and
which often bears eyes, tentacles, and sensory palps.
• The peristomium surrounds the mouth and may bear setae, palps, or, in
predatory forms, chitinous jaws.
• The polychaete trunk is segmented, and most segments bear parapodia, which
may have lobes, cirri, setae, and other extensions. Parapodia typically are used in
crawling.
• They usually serve as the chief respiratory organs, although some polychaetes
also have gills.
Nutrition
• Errant polychaetes are usually predators and scavengers.
• A polychaete’s digestive system consists of a foregut, a midgut, and a hindgut.
• The foregut includes a mouth, a pharynx, and an oesophagus.
• It is lined with cuticle, and the jaws, where present, are constructed of cuticular protein.
• The more anterior portions of the midgut secrete digestive enzymes but absorption occurs
toward the posterior end.
• A short hindgut connects the midgut to the exterior via the anus, which is on the pygidium.
Circulation and Respiration
• Polychaetes show considerable diversity in both circulatory and respiratory structures.
• As previously mentioned, parapodia and gills serve for gaseous exchange in various species.
• However, in some polychaetes there are no special organs for respiration, and gaseous exchange occurs
across the body surface.
• The circulatory pattern varies greatly.
• In Nereis a dorsal longitudinal vessel carries blood anteriorly, and a ventral longitudinal vessel conducts it
posteriorly (see Figure 17.2D).
• Blood flows between these two vessels via segmental networks in the parapodia and septa, and around the
intestine.
• In the burrowing predatory worm Glycera (Gr. Glykera, a feminine proper name) the circulatory system is
reduced and joins directly with the coelom.
• Septa are incomplete in this animal, and thus the coelomic fluid assumes the function of circulation.
• Many polychaetes have respiratory pigments such as hemoglobin, chlorocruorin, or hemerythrin.
Excretion
• Excretory organs consist of protonephridia and mixed proto and metanephridia in some, but most
polychaetes have metanephridia.
• There is one pair per segment, each ending with a nephrostome that opens into a coelomic
compartment.
• Coelomic fluid passes into the nephrostome, and selective resorption occurs along the nephridial
duct.
Nervous System
• Organisation of the central nervous system
in polychaetes follows the basic annelid
plan (see Figure 17.24).
• Dorsal cerebral ganglia connect with a
subpharyngeal ganglion via
acircumpharyngeal connective.
• A double ventral nerve cord courses the
length of the worm, with metamerically
arranged ganglia.
Sense Organs
• Sense organs are highly developed in polychaetes and include eyes, nuchal organs, and
statocysts
• Eyes, when present, may range from simple eyespots to well-developed organs.
• Eyes are most conspicuous in errant worms.
• Usually the eyes are retinal cups, with rodlike photoreceptor cells (lining the cup wall)
directed toward the lumen of the cup.
• The highest degree of eye development occurs in the family Alciopidae, which has large,
image-resolving eyes similar in structure to those of some cephalopod molluscs, with cornea,
lens, retina, and retinal pigments. Alciopid eyes also have accessory retinas, a characteristic
independently evolved by deep-sea fishes and some deep-sea cephalopods.
• The accessory retinas of alciopids are sensitive to different wavelengths. The eyes of these
pelagic animals may be well adapted to function because penetration by the different
wavelengths of light varies with depth. They are sensitive to dim light of the deep sea.
• Nuchal organs are ciliated sensory pits or slits that appear to be chemoreceptive, an
important factor in food gathering.
• Some burrowing and tube-building polychaetes have statocysts that function in body
orientation.
• Polychaetes have no permanent sex organs, and
they usually have separate sexes.
Reproduction and
Development
• Reproductive systems are simple: gonads appear as
temporary swellings of the peritoneum and shed
their gametes into the coelom.
• The gametes are then carried to the outside
through gonoducts, through the metanephridia, or
by rupture of the body wall.
• Fertilization is external, and the early larva is a
trochophore (see Figure 16.7
Adaptation and
Physiology
•
ADAPTATION AND PHYSIOLOGY
Swarming Sexual Stages
•
Some polychaetes live most of the year as sexually immature animals
called atokes, but during the breeding season a portion of the body
becomes sexually mature and swollen with gametes (Figure 17.8).
•
An example is the palolo worm, which lives in burrows among coral
reefs.
•
During the swarming period, the sexually mature portions, now called
epitokes, break off and swim to the surface.
•
Just before sunrise, the sea is literally covered with them, and at
sunrise they burst, freeing eggs and sperm for fertilization.
•
Anterior portions of the worms regenerate new posterior sections.
Adaptation and
Physiology
• Swarming is of great adaptive value because
the synchronous maturation of all the
epitokes ensures the maximum number of
fertilized eggs.
• However, this reproductive strategy is very
hazardous; many types of predators have a
feast on the swarming worms.
• In the meantime, the atoke remains safely in
its burrow to produce another epitoke at the
next cycle.
• In some polychaetes, epitokes arise from
atokes by asexual budding (Figure 17.9) and
become complete worms.
Representative members of Errantia
Sedentaria
• Sedentaria contains many polychaetes and oligochaetes that live in tubes or burrows, including members of
the former phyla Pogonophora and Echiura. It also includes members of Clitellata.
• The body plan of sedentary polychaetes is much like that of errant polychaetes, except that that the head is
often modified by the addition of tentacles used for food capture.
• Parapodia are usually small and sometimes are modified to help anchor the worm in the tube; setae may be
hooklike to attach to the tube wall.
• Parapodia may function in respiration, but many tube-dwellers also have gills. Amphitrite (Gr., a mythical sea
nymph), for example, has three pairs of branched gills and long extensible tentacles (Figure 17.12). Arenicola
(L. arena, sand, + colo, inhabit), the burrowing lugworm (Figure 17.13), has paired gills on certain segments.
• Another modification is the dual use of tentacles on the head in food capture and in respiration for some
tube-dwellers (Figure 17.4).
• The expanded surface area afforded by branching within the tentacles is useful for both functions.
Representative members of Sedentaria
Clade Clitella
• Clade Clitellata contains earthworms and their relatives as well as leeches in class Hirudinida.
• Members of this clade share a unique reproductive structure called a clitellum.
• The clitellum is a ring of secretory cells in the epidermis that appears on the worm’s exterior as a
fat band around the body about one-third of the body length from the anterior end.
• The clitellum is always visible in oligochaetes, but it appears only during the reproductive season
in leeches.
• Members of Clitellata lack parapodia, presumably an evolutionary loss from a polychaete
ancestor.
• Clitellates are all hermaphroditic (monoecious) animals that exhibit direct development: young
develop inside a cocoon secreted by the clitellum, so no trochophore larva is visible.
• Small worms emerge from cocoons.
Oligochates
• Oligochaetes do not form a monophyletic group.
• More than 3000 species of worms with an oligochaete body plan occur in a great variety of sizes
and habitats.
• They include the familiar earthworms and many species that live in freshwater.
• Most are terrestrial or freshwater forms, but some are parasitic, and a few live in marine or
brackish water.
• With few exceptions, oligochaetes bear setae, which may be long or short, straight or curved,
blunt or needlelike, or arranged singly or in bundles.
• Whatever the type, setae are less numerous in oligochaetes than in polychaetes, as is implied by
the class name, which means “few long hairs.”
• Aquatic forms usually have longer setae than do earthworms.
Form and Function
• The main features of an oligochaete body are described with reference to the familiar earthworm.
• The circulatory system and excretory structures described in earthworms are typical of annelids in
general, but the digestive and nervous systems have aspects specific to oligochaetes.
• Earthworms, sometimes called “night crawlers,” burrow in moist, rich soil, and usually live in
branched, interconnected tunnels.
• The species commonly studied in laboratories is Lumbricus terrestris (L. lubricum, earthworm).
• It ranges in size from 12 to 30 cm long (Figure 17.21) but is small in comparison to giant tropical
forms whose 4 m long bodies may comprise 150 to upward of 250 segments.
• Earthworms normally emerge at night, but in damp, rainy weather they stay near the surface,
often with mouth or anus protruding from the burrow.
• In very dry weather they may burrow several feet underground, coil in a slime chamber, and
become dormant.
Form and Function
• Earthworms use peristaltic movement .
• In the central segments of the body, the longitudinal muscles contract to make the segments
short and wide, pushing against the sides of the burrow.
• As they do so, setae project outward through small pores in the cuticle.
• Setae dig into the walls of the burrow to anchor the segments.
• In the segments in front of the anchor, the circular muscles contract, extending the body.
• These anterior segments then change shape to become anchors.
• When contractions of the longitudinal muscles shorten each segment, the rest of the body is
drawn forward.
• Repeated waves of extension and contraction pass along the entire body moving the worm ahead
Form and Function
• The paired epidermal
setae
of
oligochaetes are set in a sac within the
body wall and moved by muscles (Figure
17.22), as they are in polychaetes.
• However, oligochaetes do not have
parapodia; instead, the setae extend
directly out of the body wall on each
segment.
• In most earthworms each segment bears
four pairs of chitinous setae (Figure
17.21C), although there may be more than
100 such setae per segment in some
oligochaetes.
Nutrition
• Most oligochaetes are scavengers.
• Earthworms feed mainly on decaying organic matter, bits of leaves and vegetation, refuse,
and animal matter.
• After being moistened by secretions from the mouth, food is drawn inward by the sucking
action of their muscular pharynx.
• The liplike prostomium aids in manipulating food into position.
• Calcium from soil swallowed with food tends to produce a high blood calcium level.
• Calciferous glands along the esophagus secrete calcium ions into the gut and so reduce the
calcium ion concentration of their blood.
• Calciferous glands also function in regulating acid-base balance of body fluids.
Nutrition
• Leaving the esophagus, food is stored temporarily in the thinwalled crop before being passed on
to the gizzard, which grinds food into small pieces.
• Digestion and absorption occur in the intestine.
• The wall of the intestine is infolded dorsally to form a typhlosole, which greatly increases the
absorptive and digestive surface (Figure 17.21C).
• Surrounding the intestine and dorsal vessel and filling much of the typhlosole is a layer of
yellowish chloragogen cells (Gr. chlōros, green, + agōgē, a carrying away).
• This tissue serves as a center for synthesis of glycogen and fat, a function roughly equivalent to
that of liver cells.
• When full of fat, chloragogen cells are released into the coelom where they float freely as cells
called eleocytes (Gr. elaio, oil, + kytos, hollow vessel [cell]), which transport materials to the body
tissues.
• Eleocytes can pass from segment to segment and may accumulate around wounds and
regenerating areas, where they break down and release their contents into the coelom.
• Chloragogen cells also function in excretion.
Circulation and Respiration
• Annelids have a double transport system: coelomic fluid and a closed circulatory system.
• Food, wastes, and respiratory gases areclosed circulatory system.
• Food, wastes, and respiratory gases are carried by both coelomic fluid and blood in varying degrees.
• Blood circulates in a closed system of vessels, which includes capillary systems in the tissues.
• Five main blood trunks run lengthwise through the body.
• A single dorsal vessel runs above the alimentary canal from the pharynx to the anus.
• It is a pumping organ, provided with valves, and it functions as a true heart.
• This vessel receives blood from vessels of the body wall and digestive tract and pumps it anteriorly into five
pairs of aortic arches.
• The function of aortic arches is to maintain a steady pressure of blood in the ventral vessel.
Circulation and Respiration
• A single ventral vessel serves as an aorta.
• It receives blood from the aortic arches and delivers it to the brain and rest of the body, providing
segmental vessels to the walls, nephridia, and digestive tract.
• Their blood contains colorless ameboid cells and a dissolved respiratory pigment, hemoglobin.
• The blood of some annelids may have respiratory pigments other than hemoglobin, as noted
previously.
• Earthworms have no special respiratory organs, but gaseous exchange occurs across their moist
skin.
Excretion
• Each segment (except the first three and
the last one) bears a pair of
metanephridia.
• Each metanephridium occupies parts of
two successive segments (Figure 17.23).
• A ciliated funnel, the nephrostome, lies
just anterior to an intersegmental septum
and leads by a small ciliated tubule
through the septum into the segment
behind, where it connects with the main
part of the nephridium.
Excretion
• Several complex loops of increasing size compose the nephridial duct,
which terminates in a bladderlike structure leading to an opening, the
nephridiopore.
• The nephridiopore opens to the outside near the ventral row of setae.
• By means of cilia, wastes from the coelom are drawn into the
nephrostome and tubule, where they are joined by salts and organic
wastes transported from blood capillaries in the glandular part of the
nephridium.
• Waste is discharged to the outside through a nephridiopore.
Excretion
• Aquatic oligochaetes excrete ammonia; terrestrial oligochaetes usually excrete the much
less toxic urea. Lumbricus produces both, the level of urea depending somewhat on
environmental conditions.
• Both urea and ammonia are produced by chloragogen cells, which may break off and
enter the metanephridia directly; or their products may be carried by the blood. Some
nitrogenous waste is eliminated through the body surface.
• Oligochaetes are largely freshwater animals, and even such terrestrial forms as
earthworms must exist in a moist environment.
• Osmoregulation is a function of the body surface and the nephridia, as well as the gut
and dorsal pores. Lumbricus will gain weight when placed in tap water and lose it when
returned to soil. Salts as well as water can pass across the integument, salts apparently
being actively transported.
Nervous System and Sense Organs
• The nervous system in earthworms (Figure 17.24) consists of a central system and peripheral
nerves.
• The central system reflects the typical annelid pattern: a pair of cerebral ganglia (the “brain”)
above the pharynx, a pair of connectives passing around the pharynx connecting the brain with
the first pair of ganglia in the nerve cord; a solid ventral nerve cord, really double, running along
the floor of the coelom to the last segment; and a pair of fused ganglia on the nerve cord in each
segment.
• Each pair of fused ganglia provides nerves to the body structures, which contain both sensory and
motor fibers.
• Neurosecretory cells have been found in the brain and ganglia of both oligochaetes and
polychaetes.
• They are endocrine in function and secrete neurohormones concerned with the regulation of
reproduction, secondary sex characteristics, and regeneration.
Nervous System
and Sense Organs
• For rapid escape movements most
annelids have from one to several very
large axons commonly called giant
axons (Figure 17.25), or giant fibers,
located in the ventral nerve cord.
• Their large diameter increases rate of
conduction and makes possible
simultaneous contractions of muscles
in many segments.
Nervous System and Sense Organs
• Simple sense organs are distributed all over the body.
• Earthworms have no eyes but do have many lens-shaped photoreceptors in their epidermis.
• Most oligochaetes are negatively phototactic to strong light but positively phototactic to weak
light.
• Many single-celled sense organs are widely distributed in the epidermis.
• What are presumably chemoreceptors are most numerous on the prostomium.
• In the integument are many free nerve endings, which are probably tactile in nature.
General Behaviour
• Earthworms are among the most defenseless of creatures, yet their abundance and wide
distribution indicate their ability to thrive.
• Although they have no specialized sense organs, they are sensitive to many stimuli.
• They react positively to mechanical stimuli when such stimuli are moderate and negatively to a
strong stimulus (such as a footfall near them), which causes them to retire quickly into their
burrows.
• They react to light, which they avoid unless it is very weak.
• Chemical responses aid them in the choice of food.
• Chemical as well as tactile responses are very important to earthworms.
• They not only must sample the organic content of soil to find food, but also must sense its
texture, acidity, and calcium content.
• Earthworms have some learning ability.
• They can be taught to avoid an electric shock and thus can develop an association reflex.
• The process is mainly one of trial and error, for earthworms often seize a leaf several times before
getting it right.
Reproduction and Development
• Earthworms are monoecious (hermaphroditic); each animal has both male and female organs
(see Figure 17.21B).
• In Lumbricus reproductive systems are found in segments 9 to 15.
• Two pairs of small testes and two pairs of sperm funnels are surrounded by three pairs of large
seminal vesicles.
• Immature sperm from the testes mature in seminal vesicles, then pass into sperm funnels and
down sperm ducts to the male genital pores in segment 15, where they are expelled during
copulation.
• Eggs are discharged by a pair of small ovaries into the coelomic cavity, where ciliated funnels of
the oviducts carry them outside through female genital pores on segment 14.
• Two pairs of seminal receptacles in segments 9 and 10 receive and store sperm from the mate
during copulation.
Reproduction and Development
• Reproduction in earthworms may occur throughout the year as long as warm, moist weather prevails at
night (Figure 17.26).
• When mating, worms extend their anterior ends from their burrows and bring their ventral surfaces
together (Figure 17.26).
• Their surfaces are held together by mucus secreted by the clitellum (L. clitellae, packsaddle) and by special
ventral setae, which penetrate each other’s bodies in the regions of contact.
• After discharge, sperm travel to seminal receptacles of the other worm via its seminal grooves.
Reproduction and
Development
• Figure 17.26 Earthworm copulation and formation of egg cocoons.
• A, Mutual insemination; sperm from genital pore (segment 15) pass along
seminal grooves to seminal receptacles (segments 9 and 10) of each mate.
• B and C, After worms separate, the clitellum secretes first a mucous tube
and then a tough band that forms a cocoon. The developing cocoon passes
forward to receive eggs from oviducts and sperm from seminal
receptacles.
• D, As cocoon slips off over anterior end, its ends close and seal.
• E, Cocoon is deposited near burrow entrance.
• F, Young worms emerge in 2 to 3 weeks.
• G, Two earthworms in copulation. Their anterior ends point in opposite
directions as their ventral surfaces are held together by mucous bands
secreted by the clitella.
Reproduction and Development
• After copulation the worms separate; each worm secretes first a mucous tube
and then a tough, chitinlike band that forms a cocoon around its clitellum.
• The cocoon slides forward along the body.
• As the cocoon passes forward, eggs from the oviducts, albumin from skin glands,
and sperm from the mate (stored in the seminal receptacles) pour into it.
• Fertilization of eggs then occurs within the cocoon.
• When the cocoon slips past the anterior end of the worm, its ends close,
producing a sealed, lemon-shaped body.
• Embryogenesis occurs within the cocoon, and the form that hatches from the egg
is a young worm similar to the adult.
• Thus, development is direct with no metamorphosis. Juveniles do not develop a
clitellum until they are sexually mature.
Representative
Oligochaetes
Hirudinida: :Leeches
• Class Hirudinida is divided into three orders, Hirudinea, the “true” leeches, and two
others that are morphological intermediates between oligochaetes and true leeches (see
Figure 17.1).
• Oligochaetes have variable numbers of segments, segments bear setae, and there are no
suckers on the body.
• True leeches (Hirudinea) have 34 segments, entirely lack setae, and possess anterior and
posterior suckers.
• Members of order Acanthobdellida have 27 segments, bear setae on the first five
segments, and have a posterior sucker.
• Members of order Branchiobdellida have 14 or 15 segments, no setae, and an anterior
sucker.
• Branchiobdellids are commensal or parasitic on crayfish.
Hirudinida: Leeches
• Hereafter, “leech” refers to members of order Hirudinea.
• Leeches occur predominantly in freshwater habitats, but a few are marine, and some
have even adapted to terrestrial life in warm, moist places.
• They are more abundant in tropical countries than in temperate zones.
• Most leeches are between 2 and 6 cm in length, but some, including “medicinal” leeches,
reach 20 cm.
• The giant of all is the Amazonian Haementeria (Gr. haimateros, bloody), which reaches
30 cm.
• Leeches are usually flattened dorsoventrally and exhibit a variety of patterns and colors:
black, brown, red, or olive green.
• Many leeches live as carnivores on small invertebrates; some are temporary parasites;
and some are permanent parasites, never leaving their host.
• Some leeches attack human beings and are a nuisance to outdoor enthusiasts.
Form and
Function
• Unlike other annelids, leeches have a fixed
number of segments but they appear to have
many more because each segment is marked
by transverse grooves to form superficial rings
(Figure 17.28).
• Leeches lack distinct coelomic compartments.
• In all but one species the septa have
disappeared, and the coelomic cavity is filled
with connective tissue and a system of spaces
called lacunae.
• The coelomic lacunae form a regular system of
channels filled with coelomic fluid, which in
some leeches serves as an auxiliary circulatory
system.
Form and Function
• Leeches are more highly specialized than oligochaetes.
• They have lost the setae used by oligochaetes in locomotion and have developed
suckers for attachment while sucking blood (their gut is specialized for storage of
large quantities of blood).
• Most leeches crawl with looping movements of the body, by attaching first one
sucker and then the other and pulling the body along the surface.
• Aquatic leeches swim with a graceful undulatory movement.
Nutrition
• Leeches are popularly considered parasitic, but many are predaceous.
• Most freshwater leeches are active predators or scavengers equipped with a
proboscis that can be extended to ingest small invertebrates or to take blood
from cold-blooded vertebrates.
• Some can force their pharynx or proboscis into soft tissues such as the gills of
fish.
• Some terrestrial leeches feed on insect larvae, earthworms, and slugs, which they
hold by an oral sucker while using a strong sucking pharynx to ingest food.
• Other terrestrial forms climb bushes or trees to reach warm-blooded vertebrates
such as birds or mammals.
Nutrition
• Most leeches are fluid feeders.
• Many prefer to feed on tissue fluids and blood pumped from
open wounds.
• Some fresh-water leeches are true bloodsuckers, preying on
cattle, horses, humans, and other mammals.
• True bloodsuckers, which include the socalled medicinal
leech, Hirudo medicinalis (L. hirudo, a leech) (Figure 17.29),
have cutting plates, or chitinous “jaws,” for cutting through
tough skin. Salivary glands secrete an anesthetic, as well as
anticoagulant enzymes (see Section 32.3:Receiving Region).
• Some parasitic leeches leave their hosts only during the
breeding season, and certain fish parasites are permanently
parasitic, depositing their cocoons on their host fish.
• However, even the true bloodsuckers rarely remain on the
host for a long period of time.
Respiration and excretion
• Gas exchange occurs only through the skin except in some fish leeches, which
have gills.
• There are 10 to 17 pairs of nephridia, in addition to coelomocytes and certain
other specialized cells that also may be involved in excretory functions.
Nervous and Sensory Systems
• Leeches have two “brains”: one is anterior and composed of six pairs of fused
ganglia (forming a ring around the pharynx); the other is posterior and composed
of seven pairs of fused ganglia.
• An additional 21 pairs of segmental ganglia occur along the double nerve cord.
• In addition to free sensory nerve endings and photoreceptor cells in the
epidermis, there is a row of sense organs, called sensilla, in the central annulus of
each segment.
• Pigment-cup ocelli also are present in many species.
Reproduction
• Leeches are hermaphroditic but cross-fertilize during copulation.
• Sperm are transferred by a penis or by hypodermic impregnation (a
spermatophore is expelled from one worm and penetrates the integument of the
other).
• After copulation their clitellum secretes a cocoon that receives eggs and sperm.
• Leeches may bury their cocoons in mud, attach them to submerged objects, or, in
terrestrial species, place them in damp soil.
• Development is similar to that of oligochaetes.
Circulation
• The coelom of leeches has been reduced by the invasion of connective tissue
and, in some, by a proliferation of chloragogen tissue, to a system of coelomic
sinuses and channels.
• Some orders of leeches retain a typical oligochaete circulatory system, and in
these the coelomic sinuses act as an auxiliary blood-vascular system.
• In other orders the traditional blood vessels are lacking and the system of
coelomic sinuses forms the only blood-vascular system.
• In those orders contractions of certain longitudinal channels provide propulsion
for the blood (the equivalent of coelomic fluid).
Adaptive Diversification
• Annelids are an ancient group that has undergone extensive adaptive diversification.
• The basic body structure, particularly of polychaetes, lends itself to almost endless modification.
As marine worms, polychaetes occupy a wide range of habitats.
• An adaptive feature in evolution of annelids is their septal arrangement of fluid-filled coelomic
compartments. Fluid pressure in these compartments is used to create a hydrostatic skeleton,
which in turn permits precise movements such as burrowing and swimming.
• Powerful circular and longitudinal muscles can flex, shorten, and lengthen the body.
• Feeding adaptations show great variation, from the sucking pharynx of oligochaetes and the
chitinous jaws of carnivorous polychaetes to the specialized tentacles and radioles of particle
feeders. The evolution of a trophosome to house the chemoautotrophic bacteria that provide
nutrients to siboglinids is an adaptation to deepsea life.
• In polychaetes the parapodia have been adapted in many ways and for a variety of functions,
chiefly locomotion and respiration.
• In leeches many adaptations (such as suckers, cutting jaws, pumping pharynx, distensible gut, and
compounds that serve as anticoagulants in saliva) relate to their predatory and bloodsucking
habits.
Adaptation and Physiology
Attracting Leeches
• Leeches are highly sensitive to stimuli associated with the presence of a prey or
host.
• They are attracted by and will attempt to attach to an object smeared with
appropriate host substances, such as fish scales, oil secretions, or sweat.
• Those that feed on the blood of mammals are attracted by warmth; terrestrial
haemadipsids of the tropics will converge on a person standing in one place.
Adaptation and Physiology
Modern Medicinal Leeches
• For centuries “medicinal leeches” (Hirudo medicinalis) were used for bloodletting
because of the mistaken idea that a host of bodily disorders and fevers were caused by
an excess of blood.
• A 10- to 12-cm-long leech can extend to a much greater length when distended with
blood, and the amount of blood it can suck is considerable. Leech collecting and leech
culture in ponds were practiced in Europe on a commercial scale during the nineteenth
century.
• Leeches are once again being used medically.
• When fingers, toes, or ears are severed, microsurgeons can reconnect arteries but not all
the more delicate veins.
• Leeches are used to relieve congestion until the veins can grow back into the healing
appendage.
Topic 9 - Nematodes
Stephanie Ghio & Mario V Balzan Ph.D.
Nematodes
9. NEMATODES. General characteristics. Biological cycles of parasitic
nematodes
Nematodes
Nematodes (nemato from the
Greek root meaning “thread”),
also known as roundworms,
are a highly diverse group of
unsegmented worms.
They are found in almost every
environment, from deep-sea
trenches to soil ecosystems
and inside animal hosts.
Nematodes
Vinegar Eel or Vinegar Worm
(Turbatrix aceti), a harmless
nematode that spawns
inside unpasteurized vinegar
and fermented apple.
The giant parasitic
nematode worm
Placentonema
gigantissima in the
placenta of a sperm whale
(Physeter macrocephalus).
Caenorhabditis elegans is a
model organism used in
genetics, neurobiology, and
aging research.
Nematodes
Nematodes belong to the
Ecdysozoa, a clade characterized by:
• A body covered by a three-layered
cuticle that undergoes molting
(ecdysis).
• Molting controlled by ecdysone.
• Absence of cilia.
Nematodes
Nematodes belong to the
Ecdysozoa, a clade characterized by:
• A body covered by a three-layered
cuticle that undergoes molting
(ecdysis).
• Molting controlled by ecdysone.
• Absence of cilia.
Nematodes
• General Characteristics
• Triploblastic, bilaterally
symmetrical, unsegmented worms
• Pseudocoelomates (fluid-filled body cavity)
• Covered by a tough, flexible cuticle that is
periodically molted
• Found in marine, freshwater, and terrestrial
environments
• Free-living and parasitic species
• Extremely abundant: over 25,000 described
species, but estimates suggest there may be
over 1 million
Nematodes - Body Structure
Triploblastic pseudocoelomates:
The body cavity is a blastocoel
(pseudocoel), which functions as a
hydrostatic skeleton.
The body is cylindrical, unsegmented,
and vermiform (worm-like)
Nematodes – Body Organization
1. Cuticle – External protective layer
2. Hypodermis – Secretes the cuticle
3. Musculature – Longitudinal muscles
only, enabling a thrashing motion
4. Digestive system – Complete, with a
mouth, intestine, and anus
5. Nervous system – Nerve ring and
longitudinal nerve cords
6. Reproductive system – Dioecious or
hermaphroditic, internal fertilization
Circulatory and respiratory systems are
absent.
Respiration occurs through general body
surface and aerobic in free-living form and
anaerobic in parasitic form.
Cuticle
•
•
The body is generally covered with thick, flexible multi-layered collagenous
cuticle that exhibits varied textures and often bears cuticle setae (hairs),
spines or annulations.
Functions: protection (especially in endoparasitic and terrestrial species),
structural support, resistance to desiccation
•
Shed and replaced in a process called ecdysis
•
Composed of collagen and other proteins
•
Cuticle consists of three layers. Cuticle
•
Is of hypodermal origin.
Hypodermis
Cuticle
Musculature and Locomotion
•
•
•
Only longitudinal muscles, no circular
muscles
Movement achieved by alternating
contractions of dorsal and ventral
muscles
Pseudocoelomic fluid acts as a
hydrostatic skeleton
Digestive System
•
Straight tube with:
o
Mouth with specialized structures
(e.g., stylets in plant parasites,
cutting plates in animal parasites)
o
Pharynx (muscular pump)
o
Intestine (simple, tube-like)
o
Anus for waste expulsion
Digestive System
Two feeding styles are present:
1. Free-living Roundworms
• Carnivorous (feed on animals that
are even
smaller)or herbivorous (feeding on
phytoplankton such as
diatoms, algae and fungi)
• Can have teeth or spear-like
structure to spear and suck out
fluids of prey.
• Ex. P. pacificus or C. elegans (an
important model organism!)
Digestive System
Two feeding styles are present:
2. Parasitic Roundworms
• Get nutrients from a host – use one-way digestive system just
like free-living roundworms.
• Many different methods of attachment/feeding – ex.
Hookworms have cutting plates that grab onto the intestinal
lining.
Hookworm under an
electron microscope (eyes
added in MS paint for effect)
Nervous System
•
•
Cerebral ganglia (nerve ring) near
the pharynx
Longitudinal nerve cords:
o
o
o
Dorsal cord (motor control)
Ventral cord (sensory and
motor functions)
Lateral cords (less developed,
mainly sensory)
• Sensory structures:
o
Papillae and sensory setae.
o
o
Ocelli (simple eyes) in some
species.
Amphids (specialized cephalic
sensory organs unique to
nematodes).
Nervous System
•
•
Cerebral ganglia (nerve ring) near
the pharynx
Longitudinal nerve cords:
o
o
o
Dorsal cord (motor control)
Ventral cord (sensory and
motor functions)
Lateral cords (less developed,
mainly sensory)
• Sensory structures:
o
Papillae and sensory setae.
o
o
Ocelli (simple eyes) in some
species.
Amphids (specialized cephalic
sensory organs unique to
nematodes).
Labial (LP) and cephalic papillae (CP) near the mouth
Nervous System
•
•
Cerebral ganglia (nerve ring) near
the pharynx
Longitudinal nerve cords:
o
o
o
Dorsal cord (motor control)
Ventral cord (sensory and
motor functions)
Lateral cords (less developed,
mainly sensory)
• Sensory structures:
o
Papillae and sensory setae.
o
o
Ocelli (simple eyes) in some
species.
Amphids (specialized cephalic
sensory organs unique to
nematodes).
Variability in the ocelli of Onchium robustum
Nervous System
•
•
Cerebral ganglia (nerve ring) near
the pharynx
Longitudinal nerve cords:
o
o
o
Dorsal cord (motor control)
Ventral cord (sensory and
motor functions)
Lateral cords (less developed,
mainly sensory)
• Sensory structures:
o
Papillae and sensory setae.
o
o
Ocelli (simple eyes) in some
species.
Amphids (specialized cephalic
sensory organs unique to
nematodes).
Nervous System
•
•
Cerebral ganglia (nerve ring) near
the pharynx
Longitudinal nerve cords:
o
o
o
Dorsal cord (motor control)
Ventral cord (sensory and
motor functions)
Lateral cords (less developed,
mainly sensory)
• Sensory structures:
o
Papillae and sensory setae.
o
o
Ocelli (simple eyes) in some
species.
Amphids (specialized cephalic
sensory organs unique to
nematodes).
Amphids are chemosensory organs that detect chemical and
thermal hues. Vary in structure and complexity.
Excretory System
•
•
Simple system with
excretory canals (no
flame cells)
Functions in
osmoregulation and
waste excretion
Excretory System
•
•
•
Simple system with
excretory canals (no
flame cells)
Functions in
osmoregulation and
waste excretion
In the class Adenophorea
glandular renette cells
with the duct.
Excretory System
• Aquatic nematodes possess glandular renette
cells, located ventrally near the pharynx. These
cells, single or multiple, connect to an excretory
pore and regulate water and ion balance.
Nitrogenous waste, primarily ammonia, diffuses
across the body wall due to their aquatic
environment.
• Parasitic nematodes have a tubular excretory
system derived from renette cells. It consists of
two longitudinal excretory canals connected by a
transverse canal, forming an H-shaped structure.
The system opens through a single ventral
excretory pore near the anterior end. In addition
to osmoregulation, it secretes substances that
modulate the host’s immune response.
Reproduction
•
•
•
•
Mostly dioecious (separate sexes Sexual dimorphism: Males are smaller
than females, with a curved posterior
end), but some hermaphroditic species
Reproductive system consists of gonads
and simple or paired ducts.
Internal fertilization.Males possess
copulatory spicules that facilitate sperm
transfer.
Egg development (oviparous):
o
o
Direct (e.g., Caenorhabditis elegans)
Indirect (larval stages in parasitic
nematodes)
Reproduction
•
•
•
•
Mostly dioecious (separate sexes Sexual dimorphism: Males are smaller
than females, with a curved posterior
end), but some hermaphroditic species
Reproductive system consists of gonads
and simple or paired ducts.
Internal fertilization.Males possess
copulatory spicules that facilitate sperm
transfer.
Egg development (oviparous):
o
o
Direct (e.g., Caenorhabditis elegans)
Indirect (larval stages in parasitic
nematodes)
head readialy symmetre
Body Symmetry: Bilaterally symmetrical
Body Shape: Cylindrical, elongated, and tapered at both ends
General
Characteristics
Body Covering: Covered by a tough, flexible, and non-cellular cuticle, which
provides protection and structural support
Body Cavity: Pseudocoelomates (have a fluid-filled body cavity that is not
fully lined by mesoderm)
Segmentation: Unsegmented
Digestive System: Complete (mouth, intestine, and anus)
Circulatory System: Absent (nutrients distributed by diffusion and
movement of fluid in pseudocoelom)
Respiratory System: Absent (gas exchange occurs by diffusion)
Excretory System: Renette cells or lateral excretory canals
Nervous System: Consists of a nerve ring around the pharynx and
longitudinal nerve cords
Reproduction: Mostly dioecious (separate sexes), with internal fertilization
Nematodes of Veterinary Importance
• Free-Living Nematodes
•
Important in soil ecosystems, nutrient cycling
• Parasitic Nematodes
•
•
Plant parasites (Meloidogyne spp., Heterodera spp.)
Animal parasites:
• Gastrointestinal parasites: Ascaris suum,
Toxocara canis, Haemonchus contortus
• Filarial worms: Dirofilaria immitis (heartworm in
dogs)
• Trichinella spiralis (causes trichinosis)
• Strongyloides spp., Ancylostoma spp.
(hookworms)
Types and Life Cycles of Nematodes
Free-living
nematodes
Types and Life Cycles of Nematodes
Plant
parasitic
nematodes
Types and Life Cycles of Nematodes
• Zooparasites - Entomopathogenic nematodes
Heterorhabditis
Steinernema
Types and Life Cycles of Nematodes
• Zooparasites - Entomopathogenic nematodes
Heterorhabditis
Steinernema
Life Cycles of Parasitic Nematodes
Direct life cycles
Ascaris lumbricoides
Eggs ingested
Life Cycles of Parasitic Nematodes
Direct life cycles
Ascaris suum
(Pig roundworm)
Eggs ingested
Causes liver and lung
damage ("milk spots"),
respiratory signs, and
poor weight gain.
Life Cycles of Parasitic Nematodes
Direct life cycles
Haemonchus contortus
(Barber's pole worm)
Eggs ingested
Causes haemonchosis,
leading to severe
anemia and death in
sheep and goats.
Life Cycles of Parasitic Nematodes
Indirect life cycles
Dirofilaria immitis
(Canine heartworm)
Requires an insect
vector
Causes heart failure
and pulmonary
hypertension,
transmitted by
mosquitoes.
Life Cycles of Parasitic Nematodes
Indirect life cycles
Dirofilaria
Filarial worms –
require an insect
vector
Types and Life Cycles of Nematodes
• Zooparasites - Entomopathogenic nematodes
Heterorhabditis
Steinernema
Symbiotic Bacteria: Photorhabdus in Heterorhabditis,
Xenorhabdus in Steinernema
Types and Life Cycles of Nematodes
• Zooparasites – Parasitic
Nematodes in Vertebrates
• Enterobiasis
https://www.cdc.gov/dpdx/enterobiasis/index.html
Types and Life Cycles of Nematodes
• Zooparasites – Parasitic
Nematodes in Vertebrates
• Lymphatic Filariasis
[Wuchereria bancrofti]
[Brugia malayi]
[Brugia timori]
https://www.cdc.gov/dpdx/lymphaticfilariasis/index.html
Types and Life Cycles of Nematodes
• Zooparasites – Parasitic
Nematodes in Vertebrates
• Dracunculiasis
[Dracunculus medinensis]
https://www.cdc.gov/dpdx/dracunculiasis/index.html
Types and Life Cycles of Nematodes
• Zooparasites – Parasitic
Nematodes in Vertebrates
• Trichinellosis [Trichinella spp.]
Larvae encysting in the muscle tissue
https://www.cdc.gov/dpdx/trichinellosis/index.html
Types and Life Cycles of Nematodes
• Zooparasites – Parasitic
Nematodes in Vertebrates
• Anisakiasis [Anisakis simplex]
https://www.cdc.gov/dpdx/anisakiasis/index.html
Topic 10. Arthropods
Mario V Balzan Ph.D.
10. ARTHROPODS. General characteristics. Structure and
importance of the cuticle. Basic elements of a segment.
Chelicerata. Mites
Introduction to
Arthropods
• Arthropods (Greek: Arthron, jointed
+ podos, feet)
• Triploblastic, bilaterally
symmetrical, protostomes,
coelomates
• Most diverse animal phylum,
evolving for over 500 million years
Body Organization
• Segmented body (metamerism)
• Tagmatization: Metameres grouped into
functionally distinct regions (tagmata)
Homomeric segmentation in which the segments are more or
less the same
Heteromeric segmentation wherein the segments differ from
one another
Body Organization
• Segmented body (metamerism)
• Tagmatization: Metameres grouped into
functionally distinct regions (tagmata)
Three body regions, or tagmata (singular: tagma): the head,
thorax, and abdomen.
• The head is specialized for feeding and sensory functions,
• the thorax for locomotion, and
• the abdomen for feeding, reproduction, and other
physiological functions.
Body Organization
• Tagmatization involves:
• Differentiation of metameres
(heteronomous segmentation)
• Loss of external segmentation
• Modification of appendages (including
reduction/loss)
Exoskeleton and Ecdysis
• Exoskeleton: Provides
protection but limits
growth, requiring molting
(ecdysis)
• Exoskeleton composed of:
• Epicuticle (5%): Proteins &
waxes, impermeable
• Procuticle (95%): Chitin &
proteins, rigid
• Molting (ecdysis)
controlled by
ecdysone
• Growth occurs in
stages between molts
Exoskeleton and Ecdysis
• Exoskeleton: Provides
protection but limits
growth, requiring molting
(ecdysis)
• Exoskeleton composed of:
• Epicuticle (5%): Proteins &
waxes, impermeable
• Procuticle (95%): Chitin &
proteins, rigid
• Molting (ecdysis)
controlled by the
hormone ecdysone
• Growth occurs in
stages between molts
• The cuticle is not a continuous ring: It is divided into plates called
sclerites, which are separated by sutures, grooves, or joints.
Sclerite - An area of the integument or a segment of an appendage which is hard or plate-like and is
usually bounded by sutures which may be flexible infoldings of the cuticula.
• The cuticle is not a continuous ring: It is divided into plates called
sclerites, which are separated by sutures, grooves, or joints.
Sclerite - An area of the integument or a segment of an appendage which is hard or plate-like and is
usually bounded by sutures which may be flexible infoldings of the cuticula.
• The cuticle is not a continuous. It is divided into plates called
sclerites, which are separated by sutures, grooves, or joints.
Molting
•
Molting animals grow in the intermolt phases, or instars, with soft tissues increasing in
size until there is no free space within the cuticle.
•
When the body fills the cuticle, the animal enters the premolt phase.
•
Growth occurs over a much longer time period than is apparent from examining the
external size of the animal. Growth of body tissues is continuous, but the molting process
is episodic.
•
During the molting process and some time before actual ecdysis, epidermal cells enlarge
considerably. They separate from the membranous layer, secrete a new epicuticle, and
begin secreting a new exocuticle.
•
Enzymes are released into the area above the new epicuticle. These enzymes begin to
dissolve old endocuticle, and soluble products are resorbed and stored within the body of
the crustacean.
•
Finally, only exocuticle and epicuticle of the old cuticle remain, underlain by new
epicuticle and new exocuticle. The animal swallows water, which it absorbs through its
gut, and its blood volume increases greatly. Internal pressure causes the cuticle to split
along preformed lines of weakness in the cuticle, and the animal pulls itself out of its old
exoskeleton.
•
Following this is a stretching of the still soft new cuticle, deposition of new endocuticle,
redeposition of salvaged inorganic salts and other constituents, and hardening of the new
cuticle.
•
During the period of molting, the animal is defenseless and remains hidden and quiescent
Jointed Appendages
• One pair per metamere, positioned latero-ventrally (on the
sides and slightly underneath the body)
• Uniramous (single branch) vs. Biramous (two branches).
Typically a biramous appendage has:
• Protopodite – basal segment attaching the limb to the body.
• Exopodite – external branch, often functioning as a gill or for
swimming.
• Endopodite – internal branch commonly serving as a walking leg or
claw.
Jointed Appendages
• One pair per metamere, positioned latero-ventrally (on the
sides and slightly underneath the body)
• Uniramous (single branch) vs. Biramous (two branches).
Typically a biramous appendage has:
• Protopodite – basal segment attaching the limb to the body.
• Exopodite – external branch, often functioning as a gill or for
swimming.
• Endopodite – internal branch commonly serving as a walking leg or
claw.
Jointed Appendages
Functional Types of Appendages
• Locomotor:
• Walking/running
• Grasping
• Jumping
• Swimming
• Digging
• Prehensile (grasping, raptorial)
• Oral appendages: Specialized
for different feeding modes
(notably in insects).
• Sensory appendages: e.g.,
antennae.
Jointed Appendages
Morphology of insect feeding appendages.
Insects have diverse mouthparts adapted
to different feeding habits:
• Biting & Chewing (Grasshoppers,
Beetles) – Strong mandibles for cutting
and grinding.
• Piercing & Sucking (Mosquitoes,
Aphids) – Needle-like stylets for
extracting fluids.
• Sponging (Houseflies) – Sponge-like
labium for absorbing liquids.
• Siphoning (Butterflies, Moths) – Coiled
proboscis for nectar feeding.
• Chewing & Lapping (Bees) – Versatile
mouthparts for chewing and liquid
intake.
Jointed Appendages
Morphology of insect feeding appendages.
Insects have diverse mouthparts adapted
to different feeding habits:
• Biting & Chewing (Grasshoppers,
Beetles) – Strong mandibles for cutting
and grinding.
• Piercing & Sucking (Mosquitoes,
Aphids) – Needle-like stylets for
extracting fluids.
• Sponging (Houseflies) – Sponge-like
labium for absorbing liquids.
• Siphoning (Butterflies, Moths) – Coiled
proboscis for nectar feeding.
• Chewing & Lapping (Bees) – Versatile
mouthparts for chewing and liquid
intake.
Jointed Appendages
Insects possess a variety of antennae types, each
adapted to their specific environmental interactions.
Here are some common forms:
• Filiform (Thread-like): Uniform, slender segments
resembling a thread; common in ground beetles.
• Moniliform (Bead-like): Rounded segments
resembling a string of beads; seen in termites.
• Serrate (Saw-like): Segments with saw-tooth
projections; found in click beetles.
• Clavate (Clubbed): Segments gradually widening
towards the tip; characteristic of carrion beetles.
• Capitate (Knobbed): Abruptly enlarged at the tip,
forming a distinct knob; typical in butterflies.
• Pectinate (Comb-like): Segments with long
projections on one side, resembling a comb; common
in male fireflies.
• Plumose (Feathery): Feather-like with fine hair-like
structures; often found in male mosquitoes.
• Geniculate (Elbowed): Characterized by a noticeable
bend or elbow; prominent in ants and weevils.
Circulatory System
• Open circulatory
system
(hemocoel)
• Hemolymph
bathes tissues
directly
Circulatory System
• Open circulatory system
(hemocoel)
• Hemolymph bathes tissues
directly
Respiratory System
• Respiration – different structures
as adaptations allowing
arthropods to thrive in diverse
environments:
• Cutaneous (small aquatic forms,
parasites)
• Gas exchange through the body
surface
• Gills (crustaceans, horseshoe
crabs)
• Allow for underwater respiration
• Tracheal system (insects and
myriapods)
• A network of air tubes delivering
oxygen directly to the tissues in
insects and myriapods
• Book lungs (arachnids)
• Stacked, leaf-like structures for gas
exchange
Respiratory System
• Respiration – different structures
as adaptations allowing
arthropods to thrive in diverse
environments:
• Cutaneous (small aquatic forms,
parasites)
• Gas exchange through the body
surface
• Gills (crustaceans, horseshoe
crabs)
• Allow for underwater respiration
• Tracheal system (insects and
myriapods)
• A network of air tubes delivering
oxygen directly to the tissues in
insects and myriapods
• Book lungs (arachnids)
• Stacked, leaf-like structures for gas
exchange
Gills in prawns - gills are typically located within the branchial
chamber, protected by the carapace, and are structured to
facilitate efficient gas exchange in aquatic environments.
Respiratory System
• Respiration – different structures
as adaptations allowing
arthropods to thrive in diverse
environments:
• Cutaneous (small aquatic forms,
parasites)
• Gas exchange through the body
surface
• Gills (crustaceans, horseshoe
crabs)
• Allow for underwater respiration
• Tracheal system (insects and
myriapods)
• A network of air tubes delivering
oxygen directly to the tissues in
insects and myriapods
• Book lungs (arachnids)
• Stacked, leaf-like structures for gas
exchange
Digestive System
• Complete digestive system:
• Stomodeum (Foregut) – Food intake & initial digestion
• Mouthparts, pharynx, esophagus
• Crop (storage), gizzard (grinding), salivary glands
• Mesodeum (Midgut) – Enzymatic digestion & absorption
• Stomach (ventriculus), gastric caeca (increases digestion efficiency)
• Proctodeum (Hindgut) – Waste processing & water reabsorption
• Intestine, rectum (compacts waste), anus
• Adaptations - insects have different mouthparts for different diets;
crustaceans have a highly specialized two-chambered stomach and
digestive glands that enhance food breakdown and nutrient absorption;
arachnids use external digestion.
Excretory System
• Excretory organs:
• Nephridia (crustaceans)
• Figure showing the antennal glands of a
crayfish. These are filtration kidneys in which
a filtrate of the blood is formed in the end
sac. The filtrate is converted into urine as it
passes down the tubule toward the bladder
• Malpighian tubules (insects, arachnids,
myriapods)
Excretory System
• Excretory organs:
• Nephridia (crustaceans)
• Malpighian tubules (insects, arachnids,
myriapods)
• Figure showing the Malpighian tubules of
insect.
A, Malpighian tubules are located at the
juncture of the midgut and hindgut (rectum)
as shown in the cutaway view of a wasp.
B, Function of malpighian tubules. Solutes,
especially potassium, are actively secreted
into upper tubules. Water and potassium acid
urate (KHUr) follow. Potassium is resorbed in
the lower tubules, and water and other solutes
are resorbed in the rectum.
Reproductive System & Development
• Dioecious (separate sexes)
• Internal or external fertilization
• Oviparous or ovoviviparous
• Direct or mixed development:
• Ametabolous (direct)
• Hemimetabolous (incomplete
metamorphosis)
• Holometabolous (complete
metamorphosis)
Figure showing the reproductive system of crickets. Sperm from the paired testes of males pass through sperm tubes (vas deferens) to an ejaculatory duct housed in the penis.
In females, eggs from the ovaries pass through oviducts to the genital bursa. At mating sperm enclosed in a membranous sac (spermatophore) formed by the secretions of the
accessory gland are deposited in the genital bursa of the female, then migrate to her seminal receptacle where they are stored. The female controls the release of a few sperm to
fertilize her eggs at the moment they are laid, using the needlelike ovipositor to deposit the eggs in the soil.
Reproductive System & Development
• Dioecious (separate sexes)
• Internal or external fertilization
• Oviparous or ovoviviparous
• Direct or mixed development:
• Ametabolous (direct)
• Hemimetabolous (incomplete
metamorphosis)
• Holometabolous (complete
metamorphosis)
Reproductive System & Development
• Dioecious (separate sexes)
• Internal or external fertilization
• Oviparous or ovoviviparous
• Direct or mixed development:
• Ametabolous (direct)
• Hemimetabolous (incomplete
metamorphosis)
• Holometabolous (complete
metamorphosis)
Nervous System & Sensory Organs
• Ganglionic, ladder-like nervous system
• Sensory organs:
• Mechanoreceptors (sensory hairs)
• Chemoreceptors (olfactory, gustatory)
• Photoreceptors (simple or compound eyes)
Arthropod Diversity
• The most
diverse and
numerous
group of
metazoans on
the planet (80%
of all species).
• Have been
evolving for over
500 million
years.
Arthropod Diversity
• They are cosmopolitan: they
have colonized the entire
planet.
• They have evolved into many
shapes and sizes.
• They have evolved to occupy
a wide variety of ecological
niches.
Arthropods of the great indoors …
https://www.researchgate.net/publication/291387931_Arthropods_of_the_great_indoors_Charact
erizing_diversity_inside_urban_and_suburban_homes
Major Arthropod Groups
• Chelicerates
(arachnids,
horseshoe
crabs)
• Crustaceans
• Hexapods
(insects)
• Myriapods
(centipedes,
millipedes)
Chelicerates - Body Organization
• Two functional regions:
• Prosoma
(cephalothorax)
• Houses sensory organs,
mouthparts and legs
• Opisthosoma
(abdomen)
• Contains vital organs for
digestion, reproduction,
respiration and excretion
Chelicerates - Body Organization
• Two functional regions:
• Prosoma
(cephalothorax)
• Opisthosoma
(abdomen)
• Appendages:
• 1st pair: Chelicerae
(grasping, prey capture)
• 2nd pair: Pedipalps
(sensory, locomotion)
• 4 pairs of walking legs
Chelicerates - Body Organization
• Opisthosoma
• variable number of metameres (body
segments), up to 12 in some species.
• Over evolutionary time, there has
been a reduction in the number and
complexity of appendages in this
body region. However, some
specialised structures remain:
• Pectines (Scorpions):Unique sensory
organs found on the underside of the
opisthosoma. Act as
mechanoreceptors and
chemoreceptors, helping detect
vibrations and chemical cues in the
environment.
• Essential for navigation, prey
detection, and mating behavior.
Chelicerates - Body Organization
• Opisthosoma
• variable number of metameres (body
segments), up to 12 in some species.
• Over evolutionary time, there has
been a reduction in the number and
complexity of appendages in this
body region. However, some
specialised structures remain:
• Spinnerets (Spiders): Specialized silkproducing organs located at the
posterior end of the opisthosoma.
Used for spinning webs, constructing
egg sacs, making draglines, and
wrapping prey.
• Composed of multiple silk glands,
each producing different types of silk
for various functions.
• Found in different numbers across
spider species, typically ranging from
two to four pairs.
Chelicerates
• Chelicerate arthropods are an
ancient group that includes
eurypterids (extinct), horseshoe
crabs, spiders, ticks and mites,
scorpions, and sea spiders.
• Characterized by having six pairs of
appendages that include a pair of
chelicerae, a pair of pedipalps, and
four pairs of walking legs (a pair of
chelicerae and five pairs of walking
legs in horseshoe crabs).
• Have no mandibles and no antennae.
Most chelicerates suck liquid food
from their prey.
Chelicerates
• Primarily terrestrial (except for horseshoe crabs and
pycnogonids).
• The majority are walking forms but some spiders are capable of
jumping.
• Horseshoe craforms, to swim.
Chelicerates - Feeding
• They are predators: they capture prey using chelicerae and pedipalps.
• External digestion: they ingest only liquefied food after breaking down
their prey externally with digestive enzymes.
• Diverse hunting strategies:
• Active pursuit (chasing prey).
• Ambush predation (waiting for prey).
• Web-based capture (trapping prey in silk structures).
• Venom glands: used to immobilize or kill prey.
• Some species are detritivores or herbivores, feeding on decaying
organic matter or plant material.
• Parasitic blood-feeding forms: have modified mouthparts adapted for
feeding on host blood (e.g., ticks and some mites).
Chelicerates - Reproduction
• Separate sexes and sexual dimorphism.
• Elaborate mating rituals.
• Internal fertilization, either direct or indirect (via spermatophores).
• Oviparous or ovoviviparous.
• Parental care, direct development.
Chelicerates - Reproduction
• Taxonomic groups:
Chelicerate Diversity
• Arachnida (spiders, scorpions, mites)
• Merostomata (horseshoe crabs)
• Pycnogonida (sea spiders)
Arachnida
The class Arachnida is divided into 12-13 different orders
including the major groups:
• Acari (mites and ticks – often classified into a
superorder and divided into two or more orders)
• Amblypygi (tailless whip scorpions)
• Araneae (spiders)
• Opiliones (harvestmen or daddy longlegs)
• Palpigradi (micro whip scorpions)
• Pseudoscorpiones (pseudoscorpions)
• Ricinulei (hooded tick-spiders)
• Schizomida (short-tailed whip scorpions)
• Scorpiones (scorpions)
• Solifugae (camel spiders)
• Thelyphonida (whip scorpions or vinegaroons)
In addition, some recent research also places the Xiphosura
(horseshoe crabs) into the class Arachnida.
https://www.americanarachnology.org/about-arachnids/arachnid-orders/
Cl: Arachnida. O:
Scorpiones (Scorpions)
• Found on all continents, in warm
and temperate regions.
• Generally terrestrial with nocturnal
habits.
• Approximately 1,200 species.
• Predators of insects and spiders.
Cl: Arachnida.
O: Scorpiones
(Scorpions)
• External Morphology
• Prosoma and opisthosoma are
broadly connected without a
distinct waist.
• The opisthosoma is divided
into:
• Mesosoma (body)
• Metasoma (tail), which
are clearly differentiated.
• Telson (stinger):
contains a venom
gland.
Cl. Arachnica. Or:
Araneae (Spiders)
Found all over the planet, in almost all
terrestrial habitats. Some are
aquatic.
• 40,000 known species, but it is
estimated that there may be over
170,000.
• Predators of insects, using various
hunting strategies:
•
•
•
•
Active pursuit (chasing prey).
Ambush predation (waiting for prey).
Jumping to capture prey.
Web-building to trap prey.
Cl. Arachnica.
Or: Araneae
(Spiders)
External Morphology
Distinct contriction between
the prosoma and
opisthosoma.
Unsegmented opisthosoma,
containing spinnerets.
Eight eyes, with arrangement
varying by species.
Cl. Arachnica. Or: Acari
(Mites)
• The most diverse group of
chelicerates (~50,000 species).
• Mostly terrestrial, but found
worldwide, from high mountains to
ocean ridges.
• Includes free-living and parasitic
species, both aquatic and
terrestrial.
• The most medically and
economically significant arachnids.
Cl. Arachnica.
Or: Acari (Mites)
• Small, unsegmented body externally;
metameres are not visible
• Complete fusion of the prosoma and
opisthosoma, forming a single structure.
• Visible body regions:
• Gnathosoma (mouthparts region).
• Idiosoma (main body containing legs
and organs).
• Modified chelicerae and pedipalps,
fused to form the rostrum (feeding
structure).
Cl. Arachnica. Or: Acari (Mites)
• Blood-feeding ectoparasites of vertebrates.
• E.g.: Ixodes scapularis (black-legged tick, vector of Lyme disease).
• Low host specificity, meaning they can feed on a wide range of
animals.
• E.g.: Rhipicephalus sanguineus (brown dog tick, affects dogs, cattle, and
humans).
• Vectors of numerous diseases, including viruses, protozoa, fungi, and
bacteria.
• E.g.: Dermacentor variabilis (American dog tick, transmits Rocky Mountain
spotted fever).
• E.g.: Amblyomma americanum (lone star tick, associated with Ehrlichiosis and
Alpha-gal syndrome).
Sarcoptes scabiei (causes sarcoptic mange
in dogs, cats, livestock, and scabies in
humans; burrows into the skin, leading to
intense itching and dermatitis).
Varroa destructor (Varroa mite), a major pest of
Apis mellifera (European honeybee); weakens
bees by feeding on their hemolymph and
transmitting viruses.
CRUSTACEANS
Basic Organization, Reproduction and Development, Groups of Veterinary Interest
ZOOLOGY 2025
Michela Aquilina
MCAST - UAB
BASIC ORGANIZATION
Body Structure
Crustaceans are invertebrates under the phylum
Arthropoda. They are mainly aquatic, with many
marine species.
They have a segmented body divided into three
main parts: head (cephalon), thorax (pereon), and
abdomen (pleon). The head and the thorax may be
fused to form the cephalothorax, which may be
covered by a single carapace.
They exhibit a hard exoskeleton composed of chitin
and calcium carbonate, which provide protection
and must be molted as they grow.
BASIC ORGANIZATION
Appendages and Locomotion
Crustaceans have joint appendages which
are adapted for various functions:
Antennae: Two pairs of antennae which provide the primary sensory
interface with the environment
Mandibles: A pair of mandibles which are used in handling food.
Maxilliped, which are small legs surrounding the mouth, aid in feeding.
5 pairs of legs: They are known as decapods. These include the
chelipeds (claws) which are used for protection and hunting.
Swimmerets: A series of small appendages found beneath the
abdomen and aid in forward swimming.
BASIC ORGANIZATION
Respiratory and Circulatory Systems
Respiratory system
Very small crustaceans exchange gases via
di usion directly across the body surface, called
the integument. This is feasible as their oxygen
requirements are very low, and they have a big
surface area to body ratio. Examples: Copepods,
Isopods, Ostracods
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Larger crustaceans primarily use gills for
respiration. The gills contain membranes that
bind to dissolved oxygen in the water as water
passes over them, and it moves from the gills into
the heamolymph. Examples: Crabs, Lobsters,
Cray ish
BASIC ORGANIZATION
Respiratory and Circulatory Systems
Open Circulatory System
Like other arthropods, blood lows in sinuses
with no de initive walls. Many small primitive
crustaceans, like ostracods, have no heart,
meaning blood lows is maintained by body
movement. If the heart is present, it is situated
in the pericardium with which it communicates
by ostia (paired valvular openings).
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In larger crustaceans such as the lobster, main
vessels are present, although reduced. These
carry blood pumped by the heart into the
hemocoel, where it comes into contact with
organs so that nutrient and gas exchange may
occur.
BASIC ORGANIZATION
Digestive System
The digestive tract is usually a direct passage through the body. In most species it is straight, with the
exception of some water leas (Anomopoda) where it is coiled.
The foregut varies with species, some having a simple tube and others having a complex gastric mill,
which is a chitinized grinding structure made up of a set of calci ied plates (ossicles) . This specialized
structure aids in the breakdown of food particles.
At the junction of the foregut and the midgut, a ilter of setae is found, which ilters th passing food
particles.
The midgut contains diverticula, which art digestive pouches. These help break down and absorb food.
Their complexity depends on the species.
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The hindgut is short, and lined with a cuticle for protection. It ends at a muscular anus with dial actor
muscles that help to control waste expulsion.
BASIC ORGANIZATION
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Internal anatomy of a cray ish and a crab
BASIC ORGANIZATION
Excretory System
Crustaceans have two excretory organs:
• Antennal glands
• Maxillary glands
Both have a similarly structure consisting of an end sac, a
coiled duct, and sometimes a bladder. They function to
regulate salt and water balance in the body, and the antennal
gland is also capable of re absorbing glucose to maintain
energy needs.
Nitrogen waste excretion
Most crustaceans are able to excrete ammonia through their
Gil’s. Terrestrial species, such as land crabs, produce urea
which is less toxic and may be stored in urate cells, found in
the connective tissues near the bases of the legs. This helps
terrestrial species limit water loss.
BASIC ORGANIZATION
Nervous System and Sensory Organs
Nervous system: Consists of a brain connected to a ventral nerve cord
with multiple ganglia (nerve centers). In primitive species such as
fairy shrimp, the antennae nerves come from a ring around the
esophagus. In advanced species, these nerves originate directly from
the brain. The sub-esophageal ganglion forms the fused nerve
centered of the mandibles and maxillae. Some species such as crabs
and barnacles fuse all ventral ganglia into a central mass.
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Vision: crustaceans have compound eyes
consisting of hundreds of small units. Pigment
cells are present to adjust to di erent light levels,
helping the animals to see in varied lighting.
Some crustaceans have a medium eye in their
larval stages.
BASIC ORGANIZATION
Nervous System and Sensory Organs
Crustaceans have a number of sensory organs to help them
interact with and respond their environment.
- Setae: Hair like structures which detect physical and chemical
stimuli. Tactile setae sense touch and movement, while
chemosensory setae detect chemical signs. They are found on
antennules and mouthparts.
- Statocysts: Can be described as balance organs, and help with
orientation and movement. They are located at the bases of
antennules. Statocysts contain statoliths, which are small
granules that shift to detect body position changes
REPRODUCTION AND DEVELOPMENT
Sexual Reproduction and Parthenogeneiss
Crustacean species have separate sections, but barnacles are hermaphroditic,
possessing both male and female organs. In some species such as Pandalus montagui,
the individuals are able to change sex during their life. This happens from male to
female after 13 months.
Males are often smaller than females, exhibiting sexual dimorphism, as seen in parasitic
copepods. However in decapods, the opposite is true with males having larger pincers
and an overall larger body. Males have modi ied appendages for sperm transfer, such as
clasping organs and spermatophores.
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Normal sexual reproduction involves the fusion of a sperm with an egg, but some
crustaceans are parthenogenetic, producing eggs that develop without th ended of
fertilization. Many brachiopods exhibit this characteristic.
REPRODUCTION AND DEVELOPMENT
Egg Release
Egg release varies across species:
- Cocepods and some malacostracans release eggs freely into the water.
- Decapods carry their eggs by abdominal appendages, and are secured by seta, which secrete a
cement like substance to bind the eggs
Brood pouches are common in isopods, decapods, amphipods, and branchiopods. The carapace forms a
pouch to protect the eggs. This reproductive strategy ensures that the eggs are kept Safe until hatching.
Cocepods carry their eggs in sacs attached to the abdomen.
REPRODUCTION AND DEVELOPMENT
Larval Development
Most crustaceans hatch as nauplius larvae, characterized by a simple unsegmented body with three
pairs of appendages - antennae, antennules, and mandibles - and a single naupliar eye
The development process varies across species:
Cocepods undergo 5 molts, and then transform into copepodids which resemble adults. Limbs are
added in subsequent molts.Barnacle larvae pass through a ciprid stage, which is free living. Once th
ecyprid attaches to a solid surface, it undergoes metamorphisms to an adult barnacle, where the
other appendages grow. Decapod Larvae hatch as zoeae, which are spiny small larvae. These later
develop into magalops, which is their small crab stage.
Crustaceans must replace their exoskeleton with each molting phase. They do this by producing a
soft, new one beneath the old exoskeleton, during molting, the old exoskeleton splits and the
crustacean emerges, expanding its body size before the new exoskeleton hardens.
GROUPS OF VETERINARY
INTEREST
Cocepods
Cocepods are small crustaceans found in marine, freshwater, and
terrestrial environments.
Many species are ectoparasites of ish, such as sea lice
(Lepeophtheirus salmonis). Copepods play a role in pathogenesis,
and can cause abrasion and in lammation on the hosts skin, e ecting
gill function and causing infections. These parasites can also
signi icantly harm ish by causing anemia and reducing growth rates.
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Some copepods serve as vectors for protozoan parasites (example
Cryptocaryon spp).
GROUPS OF VETERINARY
INTEREST
Isopods and Branchiopods
Isopods can be parasitic, attaching to the gills, mouths, and skin of ish and marine mammals such as
dolphins and whales. They feed on the hosts skin tissue which results in tissue necrosis and causes
secondary infections. This causes major health problems and can lead to death due to extensive
tissue damage.
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Branchiopods included water leas (Daphnia spp), and while non parasitic, they can act as vectors for
bacterial and viral infections in ish. An example of a virus carried by branchiopods is the white spot
syndrome virus. Although they can indirectly cause harm, they are a key component of the aquatic
food chain
GROUPS OF VETERINARY
INTEREST
Veterinary Concerns Regarding Crustaceans
Parasitic crustaceans: Many marine crustaceans act as ectoparasites on ish,
other crustaceans, and marine animals. Copepods and Isopods are commonly
seen, and cause anemia and secondary infections. Infected hosts may su er
from reduced growth rate and immunosuppression.
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Pathogen transmission: Crustaceans can act as vectors for protozoans,
myxozoans, and bacterial pathogens both in wild and aquaculture
environments. Control measures to prevent the spreading of any carrying
diseases and viruses include quarantine procedures, improved water
management, and targeted treatment such as antifungal or antibacterial
compounds. These measures are essential for disease control in aquaculture
systems.
Insects
Hexapoda
Hexapoda
●
●
A subphylum named for the presence of 6
legs.
2 subclasses:
○ Entognatha: Have entognathous
mouthparts
○ Insects: Have ectognathous
mouthparts
Body Structure
Head
Contains sensory
organs & mouthparts
Abdomen
Segmented.
Contains the
digestive, excretory &
reproductive organs
Thorax
3 segments:
Prothorax,
mesothorax &
metathorax.
Each segment has a
pair of jointed legs.
If present, wings are
found on the
meso/metathorax.
Body Structure
Exoskeleton
Composed of chitin.
Antennae
Tactile & olfactory
sensory organs
Wings
Extensions of the
epidermis
Legs
Jointed
Digestive System
●
●
●
●
Digestive enzymes break down food into nutrients that can be absorbed through the gut
lining.
Foregut (Stomodeum): for ingestion & storage
○ Includes the mouth, pharynx, oesophagus, crop (storage) and proventriculus (for
grinding food).
Midgut (Mesenteron): for digestion & absorption
○ Lacks a cuticle lining, allowing for direct interaction of food with digestive enzyme
Hindgut (Proctodeum): for excretion
○ Ileum, colon & rectum.
○ Responsible for water and ion absorption, leading to faeces formation.
Respiratory System
●
●
●
●
Tracheal system
○ Network of tubes that deliver oxygen directly to tissues
Air enters via spiracles located along the thorax & abdomen.
Spiracles lead to tracheae which branch into finer tracheoles.
Air sacs to allow organ growth & movement.
Circulatory System
●
●
●
Open circulatory system
Hemolymph flows within hemocoel.
○ Hemolymph carries nutrients, hormones & waste products.
Heart and aorta make up a dorsal vessel, which facilitates hemolymph movement.
Nervous System
●
●
●
●
●
Ventral nerve cord with ganglia
Giant fiber system & neurosecretory cells
Sensilla for mechanical stimuli
Tympanal organs detect sound
Chemoreceptors regulate behavior
Vision & Sensory Perception
●
●
Simple eye (Ocelli): Found in some
adult insects. Thought to be there to
help detect photoperiod.
Compound eye: Thousands of
ommatidia. More UV-sensitive than
human eyes.
Excretory System
●
●
●
Malpighian tubules: Attach at midgut-hindgut region.
Remove waste
Mechanism: Proton pump secretes H+ ions which are
exchanged for K+ ions. This exchange draws water in
osmotically.
Nitrogenous waste: Uric acid.
Insect flight
Muscles
Direct Flight
Muscles
Indirect Flight
Muscles
Attach to wings for
precise movements
Deform the thorax
to move the wing
Types of Movement
Synchronous
Flight
Asynchronous
Flight
One nerve impulse
per wingbeat
One impulse
triggers multiple
beats.
Development
Fertilization & Egg
Development:
Internal fertilization.
Eggs laid in clutches
or singularly.
Hatching:
Larva or nymph
emerges.
First instar begins at
hatching.
Molting:
AKA Ecdysis.
Required for growth.
Multiple growths for
gradual development.
Metamorphosis
Ametabolous
Development
Hemimetabolous
Development
Holometabolous
Development
AKA No Metamorphosis
AKA Incomplete
Metamorphosis
AKA Complete Metamorphosis
Seen in wingless, primitive
insects.
Stages:
Egg → Juvenile → Adult
Juvenile resembles adult,
except with regard for
reproductive maturity.
Continuous growth throughout
life.
Multiple molts.
Stages:
Egg → Nymph → Adult
Nymph resembles adult, but
lacks fully developed wings &
reproductive organs.
Final molt produces a fully
mature, winged adult.
Most common form of
development
Stages:
Egg → Larva → Pupa → Adult
Holometabolous Development
Larval Stage
●
●
Larvae specialized for
feeding & growth.
Easy to distinguish
from adult form &
lack wings.
Grow larger through
multiple instars
before pupation
Adult Stage
Pupal Stage
●
●
Non-feeding inactive
stage where
metamorphosis
occurs.
Larval tissues broken
down & reorganised.
●
●
Fully formed adult
with fully developed
wings & reproductive
organs emerges.
Behavioural change:
more focus on
reproduction &
dispersion as
opposed to growth.
Insects of Veterinary Interest
Biting & Nuisance Insects
Irritation, painful bites.
Parasitic Insects
Infest animals. Can also carry disease
Myiasis Causing Flies
Infestations of larvae (maggots)
Blood sucking insects
Vectors of disease
1 Insects (Hexapoda)
Insects belong to the phylum Arthropoda and subphylum Hexapoda. They are characterized
by having six legs, a segmented body, and an exoskeleton made of chitin.
Hexapoda is divided into two classes:
●​ Entognatha – Small, primitive, wingless insects with mouthparts enclosed within the
head capsule.
●​ Insecta (True Insects) – More advanced insects with ectognathous mouthparts
(mouthparts exposed outside the head capsule).
Insecta is further categorized into:
●​ Pterygotes (Winged Insects) – Majority of insects that possess wings.
●​ Apterygotes (Wingless Insects) – Primitive, wingless insects.
The study of insects is called Entomology.
Structure of Insects
Insects have a segmented body divided into three tagmata (functional regions):
1.​ Head – Sensory and feeding structures.
2.​ Thorax – Locomotion (legs and wings).
3.​ Abdomen – Houses most internal organs.
External Features
Head (Sensory and Feeding Structures)
●​ Antennae – Sensory organs for touch, smell, and sometimes sound detection.
●​ Eyes –
○​ Compound eyes: Made of multiple ommatidia, providing a broad field of vision,
color detection (including UV light), and motion sensing.
○​ Simple eyes (ocelli): Detect changes in light intensity.
●​ Mouthparts – Adapted for various feeding habits:
○​ Labrum – Upper lip.
○​ Mandibles – Used for biting, chewing, or grasping.
○​ Maxillae – Assist in food manipulation.
○​ Labium – Lower lip, helps with manipulation.
○​ Hypopharynx – Tongue-like structure.
Thorax (Locomotion)
The thorax consists of three segments:
1.​ Prothorax – Bears the first pair of legs.
2.​ Mesothorax – Bears the second pair of legs and (if present) the first pair of wings.
3.​ Metathorax – Bears the third pair of legs and (if present) the second pair of wings.
●​ Legs – Adapted for various functions:
○​ Walking legs (e.g., ants, beetles).
○​ Jumping legs (e.g., grasshoppers).
○​ Grasping legs (e.g., mantises).
○​ Swimming legs (e.g., aquatic beetles).
●​ Wings – Thin, double-layered extensions of the cuticle, strengthened by veins.
Abdomen (Vital Organs)
●​ Segmented (9–11 segments).
●​ Contains digestive, excretory, respiratory, and reproductive systems.
●​ The 11th segment (if present) bears cerci (sensory appendages).
Internal Systems
Digestive System
The digestive system is divided into three main regions:
1.​ Foregut (Ingestion & Storage)
○​ Mouth → Pharynx → Esophagus → Crop (storage) → Proventriculus (grinding in
some species).
2.​ Midgut (Digestion & Absorption)
○​ Contains enzymes for breaking down food and absorbing nutrients.
3.​ Hindgut (Excretion & Water Absorption)
○​ Malpighian tubules remove nitrogenous waste.
○​ Rectum reabsorbs water and ions.
Circulatory System
●​ Open circulatory system (no blood vessels like in vertebrates).
●​ Hemolymph (insect "blood") is pumped by a dorsal heart through the aorta and into the
body cavity.
●​ Hemolymph functions in nutrient transport and immune defense but does not carry
oxygen.
Definitions
●​ Dorsal Heart: Tube like heart located along their back (dorsally).
Respiratory System
●​ Tracheal System – A network of tubes (tracheae) that directly transport oxygen to
tissues.
●​ Spiracles – Small openings (typically 2 pairs on the thorax and 7–8 pairs on the
abdomen) regulate airflow.
●​ Tracheoles – Microscopic branches that reach individual cells.
●​ Air sacs – Expandable tracheae that aid in ventilation.
Nervous System
●​ Ventral nerve cord with paired ganglia (mini brains) in each body segment.
●​ Giant fiber system allows for rapid reflexes.
●​ Sensory structures:
○​ Sensilla – Detect touch, vibration, and chemical stimuli.
○​ Tympanal organs – Detect sound waves (e.g., in moths and crickets).
○​ Chemoreceptors – Often located in pits; help in feeding, mating, and habitat
selection.
Definitions
●​ Ganglia: clusters of nerve cells that function as mini brains. The decentralised system
allows insects to function even if the cerebral ganglion is damaged.
●​ Giant fiber system: High speed neural circuit for “emergency” responses.
●​ Ommatidia: Compound eye units, mini independent eyes. have their own lens,
photoreceptor cells & nerve connections. collectively create a mosaic like image.
●​ Ocelli: basic light sensors present in some insects. found in threes (in a triangle) around
the forehead. helps with flight stability and orientation.
Excretory System
●​ Malpighian tubules remove nitrogenous waste.
●​ Functions via a proton pump that facilitates ion exchange, pulling water into tubules by
osmosis.
●​ Waste product: Uric acid (minimizes water loss).
Insect Flight
Mechanism of Flight
Insects are the only invertebrates capable of sustained flight.
●​ Flight muscles:
○​ Indirect flight muscles deform the thorax to generate wing movement.
○​ Direct flight muscles attach directly to the wings for precise control.
Types of Wing Movement
1.​ Synchronous Flight (One nerve impulse per wingbeat)
○​ Used by butterflies, dragonflies.
2.​ Asynchronous Flight (Multiple wingbeats per nerve impulse)
○​ Used by flies, bees (enables high-frequency wingbeats).
Development and Metamorphosis
Fertilization
●​ Internal Fertilization: Most insects exhibit internal fertilization, where the male transfers
sperm to the female through copulation or indirect sperm transfer (e.g., in some primitive
insects like silverfish).
●​ Sperm Storage: The sperm is stored in a specialized structure called the spermatheca,
allowing females to fertilize eggs over time without needing repeated mating.
●​ Parthenogenesis: In some insect species, reproduction can occur without fertilization
(e.g., aphids, certain wasps), producing offspring that are genetically identical to the
mother.
Egg Development (Oviposition & Embryogenesis)
●​ After fertilization, the zygote undergoes embryonic development inside the egg.
●​ The developing embryo is protected by a chorion, a tough outer shell that prevents
desiccation and provides mechanical protection.
●​ In ovoviviparous species (e.g., tsetse flies), eggs hatch inside the female, and she
gives birth to live larvae.
Hatching (Emergence of Larva or Nymph)
●​ Once embryonic development is complete, the egg hatches, producing either:
○​ Larvae (in insects undergoing holometabolous development, such as butterflies,
flies, and beetles).
○​ Nymphs (in insects undergoing hemimetabolous development, such as
grasshoppers and true bugs).
●​ The newly emerged form may differ greatly from the adult in structure, habitat, and
feeding habits.
Molting (Ecdysis) – Shedding of the Exoskeleton
Molting is the process by which an insect sheds its old exoskeleton to accommodate growth.
This is essential because the rigid chitinous exoskeleton does not expand.
Regulation: Molting is controlled by the neuroendocrine system and involves several
hormones, mainly ecdysone and juvenile hormone (JH).
Role of Hormones in Development
●​ Ecdysone: A steroid hormone produced by the prothoracic glands, triggering molting
and metamorphosis.
●​ Juvenile Hormone (JH): JH levels determine developmental fate:
○​ High JH levels – The insect molts into another larval or nymphal stage.
○​ Low JH levels – Metamorphosis is triggered, leading to pupation or adult
emergence.
Definitions
●​ Instar: Developmental stage between molts. Instar=new version of themselves (larger,
with more developed structures)
●​ Imago: Adulthood.
Types of Metamorphosis
1.​ Ametabolous (No Metamorphosis)
○​ Example: Silverfish.
○​ Juveniles resemble adults but lack reproductive structures.
2.​ Hemimetabolous (Incomplete Metamorphosis)
○​ Example: Grasshoppers, cockroaches.
○​ Stages: Egg → Nymph → Adult.
○​ Nymphs resemble adults but lack fully developed wings.
3.​ Holometabolous (Complete Metamorphosis)
○​ Example: Butterflies, beetles, flies.
○​ Stages: Egg → Larva → Pupa → Adult.
○​ Larvae and adults have distinct morphologies and feeding habits.
Insect Groups of Veterinary Importance
Disease Vectors (Blood-Sucking Insects)
1.​ Mosquitoes – Transmit malaria, dengue, filariasis.
2.​ Tsetse Flies – Transmit African sleeping sickness.
3.​ Sandflies – Transmit leishmaniasis.
4.​ Blackflies – Transmit river blindness.
Biting & Nuisance Insects
1.​ Stable Flies – Painful bites, transmit trypanosomiasis.
2.​ Horse Flies – Large bites, transmit Loa loa.
Parasitic Insects
1.​ Fleas – Transmit plague, tapeworms.
2.​ Lice – Cause anemia and irritation.
Myiasis-Causing Flies
1.​ Screwworm Fly – Infests livestock wounds.
2.​ Botflies – Larvae infest skin, digestive tract, or nasal cavities.
Topic 13: Echinodermata
What are
echinoderms?
The phylum Echinoderms are a diverse
group of invertebrate marine animals.
Members of this phylum include the
starfish, sea urchins, sea cucumber etc.
Classification of Echinoderms
5 Major Classes:
• Asteroidea (Starfish)
• Ophiuroidea (Brittle stars)
• Echinoidea (Sea urchins, sand
dollars)
• Holothuroidea (Sea cucumbers)
• Crinoidea (Feather stars, sea lilies)
Class Asteroidea
(Star-Like)
• ~1,500 described species.
• Central disc with five (or more) unsegmented
arms.
• Madreporite located on the aboral side.
• Example: Echinaster sp
Class
Ophiuroidea
(Snake-Like)
• ~2,000 described species.
• Highly distinct central disc.
• Five segmented arms with vertebral-like
plates.
• Incomplete digestive system (lacks an
anus).
• Closed ambulacral grooves .
• Tube feet with ampullae but without
suckers.
• Madreporite migrates to the oral side.
• Example: Ophiothrix (spiny brittle star)
Ambulacral groove- Runs along the length of each arm (or radial section) and houses tube feet
Open Ambulacral groove-Tube feet are exposed, and the groove is visible externally along the ventral (oral) side of the arms.
Closed Ambulacral groove- Groove is covered by ossicles (calcareous plates) or skin, hiding the tube feet. Adapted for
burrowing
Class Echinoidea (SpineLike)
• ~950 described species.
• Globular body, lacking a central disc or
arms.
• Many movable spines.
• Tendency toward bilateral symmetry.
• Madreporite and anus positioned on the
aboral surface.
• Possess Aristotle's lantern (internal
masticatory apparatus).
• Example: Paracentrotus lividus.
Class Holothuroidea
(Whole)
• ~1,150 described species.
• Elongated cylindrical body,
lacking a disc or arms.
• Oral-aboral axis elongated
(anterior mouth, posterior anus).
• Ossicles scattered in the dermis
(soft-bodied).
• Madreporite is internal.
• Tube feet reduced.
Class Crinoidea (LilyLike)
• ~700 described species.
• Variable number of segmented arms (5 to >200) → pinnules.
• Open, ciliated ambulacral grooves (suspension feeders).
• May have an aboral stalk (sessile species).
• Presence of cirri for attachment.
• Both mouth and anus located on the oral side.
• No madreporite.
• Comparative anatomical
diagram of different
echinoderm groups, focusing
on their radial anatomical
structures
• Cryptosyringida (Left)
Holothuroidea (sea cucumbers),
Echinoidea (sea urchins),
Ophiuroidea (brittle stars), and
Asteroidea (starfish)
• Asterozoa- Echinozoa (Right)
• Crinoidea
Body wall
• The body wall provides protection
against predators in the form of
spines and ossicles as well as
support with an endoskeleton. This
aids in the water vascular system for
movement as well as sensations
with the help of sensory cells to
detect environmental changes
Epidermis (Outer
layer)
• Thin, ciliated layer covering the
body
• Contains sensory cells, gland
cells and nerve endings
• Produces mucus and
sometimes toxins for defence
Dermis (Middle layer)
• Thick and composed of connective
tissue with calcareous ossicles
(forming the internal skeleton)
• Provides rigidity and flexibility,
depending on the species
• In some echinoderms, ossicles fuse to
form a hard test (in sea urchins) while
in others they remain separate for
flexibility (Sea stars)
Coelomic lining
(Inner layer)
• Lines the body cavity (coelom) and contains
amoeboid cells that help in immunity and wound
healing
• Assists in gas exchange and nutrient distribution
Unique features of
Echinoderms
• Radial symmetry (pentamerous in
adults)
• Water vascular system (for movement
and respiration)
• Endoskeleton made from calcium
carbonate
• Regeneration ability (ex; starfish
regenerating limbs)
Body structure and Symmetry
• In the larval stage, echinoderm larvae
have bilateral symmetry, meaning they
are mirror-imaged like humans, but as
they mature, they develop radial
symmetry.
• As they develop into adults, they undergo
metamorphosis, reorganizing their body
structure into radial symmetry, where
body parts radiate outward from a central
point.
• Most echinoderms exhibit pentamerous
symmetry, meaning their bodies are
divided into five or multiples of five
sections
The water vascular system is a unique hydraulic system found in
echinoderms, used for movement, respiration, and feeding.
Water vascular
system
•It consists of a series of interconnected canals filled with seawater, which
helps control tube feet movement through changes in water pressure.
•This system allows echinoderms to move without muscles in their limbs,
using hydraulic pressure instead.
Components of the
water vascular system
Madreporite
Stone Canal
Ring Canal
Radial Canals
Lateral Canals
Ampullae
Tube Feet (Podia)
Components of
the water
vascular system
•Madreporite – A porous,
sieve-like structure on the
dorsal surface that allows
water to enter the system.
Components of
the water
vascular system
• Stone Canal – A short
canal opening from the
ampulla that connects
the madreporite to the
ring canal. It is an S
shaped canal lined with
cilia
Components of
the water
vascular system
• Ring Canal – A circular
canal surrounding the
central disc, distributing
water to the radial
canals.
• Radial Canals –
Extend outward from
the ring canal into
each arm (in starfish)
or along the body (in
other echinoderms).
Components of the
water vascular
system
• Lateral Canals- Short, tubelike structures that connect
the radial water-vascular
canal to the tube feet
(podia) in echinoderms. They
contain one-way valves to
ensure that water flows in
the correct direction,
preventing backflow
Components of
the water
vascular system
• Tube Feet – Small,
flexible, fluid-filled
appendages connected
to the radial canals,
used for movement,
feeding, and respiration.
How the Water
Vascular system
functions
• The madreporite draws water
in
• Water flows into the stone
canal, leading to the ring canal
(around the central disk)
• From the ring canal, the radial
canals extend into each arm (in
asteroidea and Ophiuroidea)
• Lateral canals branch off from
radial canals and connect to
the tube feet
Digestive system and feeding
• Diverse digestive system and feeding habits specific to their lifestyles
and environment
• Typically these include:
• Mouth
• Oesophagus
• Stomach
• Intestine
• Anus
These vary among the different classes
Components of the digestive
system:
Mouth
• Almost all echinoderms
have mouths on the oral
(ventral)of their bodies
because of their
pentaradial symmetry.
Components of the
Digestive System:
Anus
• The anus is situated
near the centre of the
disc on the aboral
surface. This is
present in most
classes except brittle
stars (Ophiuroidea)
which expel waste
through their mouth
Components of the
Digestive system:
Oesophagus, Stomach and
Intestine
• Many species possess an
oesophagus and stomach, but
in some the pharynx opens
directly into the intestine. The
intestine is typically long and
coiled, and loops through the
body three times before
terminating in
a cloacal chamber, or directly
as the anus
Feeding Habits:
Predators
•Some echinoderms, like sea
stars (starfish), are active
predators. They use their
powerful tube feet to pry
open the shells of bivalves
(e.g., clams, mussels).
•
•Many sea stars can evert
(push out) their stomachs
through their mouths,
secreting digestive enzymes
directly into the prey before
pulling the liquefied nutrients
back into their bodies
Feeding Habits:
Suspension feeders
•Crinoids (feather stars &
sea lilies) extend feathery
arms covered in mucus and
tube feet to trap plankton
and organic particles drifting
in the water.
•These particles are then
moved toward the mouth
using tiny cilia along their
arms.
Feeding Habits: Detritivores
• Sea cucumber are primarily
detritivores, meaning they feed
on organic material found in
sediment
• They ingest sand or mud,
extract nutruents from
decaying organic matter and
expel the filtered material,
playing a crucial role in nutrient
cycling on the ocean floor
Feeding habits and Digestive adaptations Chart
Digestive
system
variations
• Complete Digestive System
(with both mouth and anus)
Found in most echinoderm,
allowing for more efficient
digestion and nutrient absorption
• Incomplete digestive system
(mouth but no distinct anus)
Seen in some brittle stars, where
waste exits through the mouth
Respiration and
excretion
• There is no specialised
respiratory organs. Gas
exchange occurs through tube
feet, papule (skin gills) or
cloacal respiration in sea
cucumbers
• They can excrete nitrogenous
waste through diffusion
Nervous System
and Sensory
Organs
• No centralised brain,
instead a nerve ring and
radial nerves which
control tube feet
• Sensory cells for
detecting light,
chemicals and touch
• Some echinoderms, like
starfish, have eye sports
at the tip of arms
Reproduction and
Regeneration
• Sexual reproduction
Echinoderms are dioecious, meaning most
species have separate male and female
individuals
Fertilization is external with both males and
females releasing eggs and sperm into the
water column
This is called Broadcast spawning, where
fertilization occurs in the open ocean,
increasing the chances of successful
reproduction
Reproduction
and
Regeneration
• Asexual Reproduction
Many echinoderms,
especially starfish, brittle
stars and sea cucumbers,
can reproduce asexually
through fragmentation
If an arm or body part is
severed, some species can
regenerate a completely new
individual if a portion of the
central disc remains
Importance of
Echinoderm
• Balance in marine ecosystems
Sea stars are keystone predators that
help regulate population of prey species,
such as muscles and sea urchins.
Without them, certain prey species
could overpopulate and disrupt marine
biodiversity
Sea urchins control algae growth on
coral reefs, preventing excessive growth
that could suffocate corals. When
predators of the sea urchin are removed,
the population explodes, leading to
habitat destruction
Importance of
Echinoderm
• Nutrient Recycling
Sea cucumbers act as ecosystem engineers by
breaking down organic material in sediment
and recycling nutrients back into the ocean.
Their waste enriches the seabed, supporting
microbial life and other bottom-dwelling
organisms
Brittle stars and crinoids aid in the breakdown
of detritus (dead organic matter), keeping the
ocean floor clean and nutrient rich
Thank you!
14. CHORDATE
Fransisca Risny Oktavia, Msc
CHORDATE
• General characteristics and basic
organization. Basic organization of
Chephalochordata. General
characteristics of the vertebrates.
FISH. Agnatha, Condrichtia and
Osteichtia. Basic organization
Structural and functional
adaptations.
CHORDATE
Animals with a dorsal
supporting rod ("chord,"
meaning string), mostly
vertebrates (backbones).
Evolutionary History – The
first chordates arose during
the Cambrian Period
approximately 550 mya.
Notochord: Flexible support rod,
replaced by vertebrae in vertebrates.
General
Characteristic
Dorsal Nerve Cord: Hollow nerve
bundle, becomes brain and spinal cord.
Pharyngeal Slits: Openings in throat,
used for filter-feeding or gills.
Post-anal Tail: Tail extension for
locomotion, often lost in adults.
Characteristics
Notochord
• (back cord) a slender rod of cartilage-like connective tissue
lying near the dorsal side of the body and extending most of the
length of the animal and runs beneath the nerve cord
• It is regarded as an early endoskeleton and has the function of
such in the protochordates.
• In more complex vertebrates, the notochord is present only
during embryo development, not during adulthood.
• In some of the less complex vertebrates, the notochord persists
throughout the life cycle and is found during embryo
development and in adult stages.
Notochord
• For those animals in which it persists into the adult form, the
notochord provides support (it acts like our backbone) and
increases swimming efficiency
• In most animals, bony structures called vertebrae develop
near the notochord and eventually replace it during
embryogenesis
Pharyngeal gill
slits
a series of paired, slender openings that connect the inside
of the pharynx/throat to the outside of the "neck".
In complex vertebrates, they appear only in the embryonic
stages.
The morphological equivalent of gill silts are seen briefly
during human development (weeks 4-5), but they usually
close or develop into other structures.
Occasionally, the slits do not close, resulting in the newborn
having an opening in the neck area (a cervical fistula).
In many chordates, the gill slits never break through from the
pharynx, but merely form pouches that have no function
Pharyngeal gill slits
• They have been modified extensively in the course of evolution.
– In primitive chordates, they serve as passageways for water into
the gills of many aquatic chordates and facilitates filter feeding in the
protochordates.
– In fishes and some amphibians, the slits bear gills and are used for
gas exchange.
– In most land - living chordates, the "gill slits" are present only in
embryonic stages; you had pharyngeal slits at one time.
– The slits are supported by gill arches, which have also been highly
modified in various groups of vertebrates
Dorsal tubular nerve cord
• A bundle of nerve fibers which runs down the "back“, lying dorsal to the
digestive tract in contrast to the ventral, solid nerve cord of most
invertebrates
• has a fluid-filled cavity with pairs of nerves branching from it at intervals and
running to the muscles.
• The anterior (forward) end of the nerve cord is often enlarged into a brain.
• along with the brain, forms the CNS.
Post-anal tail
Is the extension of the notochord and
nerve cord past the anus.
This feature may or may not persist in
the adult
serves as a means of propulsion in water;
In humans, the tail is short and fused (the
coccyx found at the base of your spine)
• – Eg. is lost in the adult stages of many chordates, such as frogs and
people.
Endostyle
• mucous secreting structure found in the pharynx floor
(traps small food particles)
Form and Function in Chordates
Nonvertebrate Chordates (like lancelets and tunicates):
• Have simple body systems, but these systems are effective for
survival.
• Their simplicity reflects an early stage of chordate evolution.
Vertebrates: Have more complex body systems.
• This complexity allows for a wider range of adaptations and ways
to live (feeding, breathing, etc.).
• The complex systems allow them to maintain homeostasis in
many different environments.
Digestive
systems of
vertebrates
• Carnivores such as sharks typically have short digestive tracts that
produce fast-acting,meat-digesting enzymes.
• Herbivores such as cows, on the other hand, often have long
intestines that harbor colonies of bacteria.These bacteria are
helpful in digesting the tough cellulose fibers in plant tissues
Respiration
• Aquatic chordates—such as tunicates, fishes, and amphibian larvae—use gills for
respiration.
• Land vertebrates, including adult amphibians, reptiles, birds, and mammals, use
lungs.
• However, some animals “break the rules.” For example, several fishes, such as
lungfishes, have both gills and lungs. As you move from amphibians to mammals,
the surface area of the lungs increases.
Circulation
• As chordates evolved, more
complex organ systems and more
efficient channels for internal
transport developed.
• Those that use gills for respiration
have a single-loop circulatory
system
• Vertebrates that use lungs for
respiration have a double-loop
circulatory system.
Response
• Brain size and complexity increase as you go from fish to
mammals.Cerebrum (thinking part):Small in fish, amphibians, and
reptiles.
• Large and complex in birds and mammals, allowing for more
advanced thinking.
• Cerebellum (movement and balance):Most developed in birds
and mammals, giving them better coordination.
Reproduction
• Chordates have many different ways to reproduce:
• Some, like the cardinalfish, have males hold eggs in their mouths.
• Others, like geese, lay eggs in nests and defend them.
• Still others, like mountain lions, give birth to live young and nurse
them with milk.
• This shows a wide range of reproductive strategies
Excretion
• Excretory systems get rid of waste (especially nitrogen waste) from the body.
• Simple chordates and fish: Use gills to get rid of waste.
• Most vertebrates:Use kidneys to filter waste from blood.
• Nitrogen waste:
Starts as toxic ammonia.
• How it's disposed of varies:
•
Aquatic animals: release ammonia directly.
•
Mammals and some others: convert it to less-toxic urea.
•
Reptiles and birds: convert it to uric acid.
• Kidneys also help balance water and salts in the body.
Basic organization of
Subphylum:Chephalochordata
• General characteristics – Lancelets are small (up to
3cm), slender organisms that bury themselves in
sediment with just their anterior end protruding
from the sediment. The lancelets contain all four
chordate characteristics as an adult.
• Unique characteristics – Lancelets lack a respiratory
system and breath through their skin
• Biogeography – Shallow temperate and tropical
seas worldwide
• Habitat – Benthic marine
• Diet – Omnivorous diet. Filter feeding on planktonic
plants and animals
General characteristics - The vertebrates are animals with
backbones and internal skeletons of made of cartilage or bone.
Vertebrates differ from other chordates in the presence of a neural
tube that forms through the fusion of the neural plate. Vertebrates
contain all four chordate characteristics as an adult with some
modifications.
Unique characteristics – They are free-living animals that diverged
from other chordates approximately 500 mya (Cambrian)
Characteristics of the
Subphylum: Vertebrates
FISH
aquatic chordates with appendages
developed as fins (when present), whose chief
respiratory organ are gills and whose body is
usually covered in scales.
There are the four major living groups of fish:
Jawless fish
Cartilaginous Fish
Lobe-finned Fish
Ray-finned Fish
Placoid
FISH SCALES
Ganoid
Ctenoid
Cycloid
Although most fishes have scales, the major groups
of fish very in the types of scales the possess.
Jawless fish lack scales, cartilaginous fish have
placoid scales, lobe-finned fish have ganoid scales
and ray-finned fish have ctenoid and cycloid scales.
All fish scales are derived from dermal tissue, which
separates them from reptile scales that are derived
from the epidermal tissue.
Fish Reproductive Strategies
In fish the fertilization of eggs can either
happen internally or externally. Internal
fertilization usually occurs through the use of
modified fins, which males use to inject
sperm. Embryo development occurs in one of
the four ways, which are categorized as the
following:
• Ovuliparity: female lays unfertilized eggs,
which are externally fertilized by the male
• Most bony fish
• Oviparity: the mother deposits internally
fertilized eggs that develop and hatch
outside of mother’s body
• Some bony fish and some sharks
• Ovoviviparity: internally fertilized eggs are
retained in oviduct, and develop without
any nourishment from the mother.
Male salmon fertilizing
eggs externally
Shark egg that was internally
fertilized
Shark embryo that was being
nourished by a yolk-sac while
being retained within the mother
• Few sharks
• Viviparity: young develop in mother’s
uterus and are nourished by the mother
before being born (live birth)
Female shark giving
live birth
• Some sharks and some bony fish
7
Superclass: Agnatha
Body structure
Rounded, eel like body. Porelike gill openings. No paired
fins. No jaws. No scales. No
internal ossification (bones)
A.
Skeletal/Muscular
1. Fibro-gelatinous notochord
-exists throughout lifecycle
-provides attachment for “W” shaped, serially arranged muscles
(myotomes)
-muscles contract to produce S-shaped eel-like movements
2. Incomplete cartilaginous skeleton
-in head, around gills & notochord
B. Respiratory/Circulatory
1. Gills
-5-16 pairs, variable number of openings (hagfish)
-7 pairs, each with external opening (lamprey)
2. Heart
-1 heart with atrium (blood holder) and ventricle (blood pumper)
-aortic arches around gills
-accessory hearts in caudal end (hagfish)
-cold-blooded (ecto-thermic)
Superclass: Agnatha
Digestive:
Mouth, pharynx, esophagus, intestine (liver), rectum, anus and
no stomach
Mouth Parts
•
Rasping tongue to grind off pieces of flesh
•
Sucker-like mouths for easy attachment
Flexibility
•
Knot tying to create more pressure against prey
Excretory/Water Balance
-primitive opisthonephridic kidneys run length of body for
regulating water balance
-pump in and out water
-(osmosis) and ions to regulate water balance
Superclass:Agnatha
Order: Myixiniformes Species:
Hagfish
General characteristics – Fish in the superclass agnatha lack scales,
jaws and paired appendages.
Unique characteristics – Hagfishes differ from lampreys in that they lack
true eyes and a stomach, and have characteristic barbels around their
mouths. Hagfish are unique in that they can secrete large quantities of
slime or mucus when attacked. Hagfish will often tie themselves in a
knot to help release the slime or to provide leverage when feeding.
Biogeography – Temperate ocean waters worldwide
Habitat – Benthic deep sea
Diet – Carnivorous diet. They are benthic scavengers that find their prey
using their sense of smell. They will often enter natural openings of
dead or dying fish and marine mammals that have sunk to the bottom
of the ocean.
Reproduction:
-separate sexes (dioecious)
-both ovaries/testes; one non-functional)
-external fertilization
-large yolky egg
-no larval stage
Barbels
Superclass: Agnatha
Order: Petromyzontiformes
Species: Lamprey
General characteristics – Fish in the superclass agnatha lack scales, jaws
and paired appendages.
Unique characteristics – The lamprey larvae, called ammocoetes, are
found in burrows in freshwater rivers and streams, where they obtain
food by filter feeding. When transitioning to the adult form the larvae
must go through metamorphosis where the entire digestive system
must be restructured.
Biogeography – Temperate marine and fresh waters worldwide
Habitat – Lampreys typically live in the ocean and must migrate up fresh
water rivers to spawn (anadromous). Ammocoetes are found in
freshwater rivers and streams.
Diet - Some adult lampreys are parasitic and feed by attaching their
mouth to a fish, secreting an anticoagulant into the host, and feeding
on the blood and tissues of the host. Ammocoetes are filter feeders.
Reproduction:
-separate sexes (dioecious)
-single gonad without duct
-external fertilization
-long larval stage:
ammocoete
Ammocoete larva
Lamprey Life Cycle
Spawn in fresh water streams
Eggs fertilized externally
Eggs hatch in 2 weeks
Larvae drift down stream and bury in fine sand
Larvae filter food out of the
water for 3 – 7 more years
Rapid metamorphosis to adult
Adults only live ~ 1 year
Class: Chondrichthyes
General characteristics – Fish in the class Chondrichthyes all lack true bone and have
a skeleton made of cartilage, which is not a primitive characteristic.
Chondricthyans have tough skin covered with placoid scales, large, buoyant livers
and spiral valve intestines.
Placoid scales
Unique characteristics – Most chondrichtyans have a highly developed sensory organ
for sensing prey called the Ampullae of Lorenzini, which helps them sense the
electrical fields given off by their prey. Male and female Chondrichthyans can be
easily distinguished by the presence or absence of claspers. Only male sharks have
claspers, which are extensions of the pelvic fins used to transfer sperm during
internal fertilization.
Evolutionary history – Fossil evidence suggests chondrichthyans diverged in
the early Devonian approximately 419 mya
Reproduction – Courtship and Copulation, Seminal fluid injected into female,
Internal fertilization, 43% lay eggs, 1 month – 2 years gestation period
Ampullae of Lorenzini
Two Chondrichtyes subclasses:
• Elasmobranchii (sharks, skates, and rays) have 5-7 gill openings, a ridged dorsal
fin and an upper jaw free from skull
• Holocehphali (chimeras) have a gill cover over a single gill opening, a spine in
front of soft dorsal fin, and an upper jaw fused to their skull
Chondrichthyes Life Cycle
Class Osteichthyes
Fish have a torpedo
shape which allows
them to reduce drag
while swimming
through the water.
They also
have the following
structures: Ctenoid
scales:embedded in
the skin
Eyes: located on the
sides with no eyelids
and they do not have
binocular vision.
Lateral line: sensitive
to pressure changes
Operculum: Hard
covering over gills
Skeletal System: axial
(skull and vertebrae)
and appendicular
(girdles and fins)
which are very flexible
for swimming
Reproduction:
Same are hermaphrodites.
Courtship (attracting males),
Spawning (gametes release
in the water, Copulation
(direct transfer of sperm)
are cold-blooded vertebrates and breathe through a pair of gills. They are covered with tough,
protective scales and have pairs of fins for swimming. Most are flattened from side to side
and have an organ called a swimbladder that helps keep them afloat.
Osteichthyes Life Cycle
Amphibians
and Reptiles
Nicole Spiteri Swain
15: Amphibians
• General Characteristics
• Anura and Caudata
15: Reptiles
Adaptations to the Terrestrial Environment
The Amniota Egg
Diversity
Amphibians
• Tetrapoda (Four Legs)
• Bilateral Symmetry
• Pedicellate (Two-Part Teeth
• Ecthothermic
Amphibians
• Amphibian comes from Greek word
amphibious which means “living a double
life” since they exploit both aquatic and
terrestrial habitats. Aquatic larval stage,
terrestrial adult stage.
• They have moist skin and rely on cutaneous
respiration
• Doubled-channelled hearing system.
• Green rods in their retinas to discriminate
hues
Pedicellate
• Pedicellate teeth are a tooth morphology unique to
modern amphibians but also seen in a variety of extinct
labyrinthodonts.
• Pedicellate teeth consists of a tooth crown and a base
(both composed of dentine) separated by a layer of
uncalcified dentine.
• Labyrinthodonts are extinct four-limbed tetrapods with
a large body size and a crocodile-like lifestyle
• Dentine is a hard dense bony tissue forming bulk of a
tooth, beneath the enamel.
Respiration
• Respiration can occur in 3 different ways:
Cutaneous Respiration, Buccal Respiration
and Pulmonary Respiration
• Most amphibians breathe through lungs and
their skin.
• Tadpole and some aquatic amphibians have
gills they use to breathe. Some examples
are axolotl, Necturus and the common
mudpuppy.
• Some amphibians do not have lungs
Cutaneous Respiration
• Takes place all the time but when the amphibian is
under water or hibernating this is the only mode of
respiration.
• Their skin needs to stay wet to absorb oxygen, so
they secrete mucous to keep their skin moist.
• Oxygen is absorbed through their skin and will enter
the blood vessels at the skin surface that will
circulate the oxygen to the rest of the body
Buccal Respiration
• Occurs when amphibian is on land.
• The mouth is permanently closed but the nostrils are open.
• The floor of buccal cavity is alternately raised and lowered.
• Air is drawn in and expelled out of the buccal cavity repeatedly
through nostrils.
• The glottis remains closed during buccal respiration so that no
air enters or leaves the lungs into buccal cavity
• The mucus epithelial lining of buccal cavity is rich in blood
capillaries which absorbs O2 and expels CO2.
• This is done to inflate the lungs.
Pulmonary
Respiration
• The breathing takes place on land.
• The lungs are poorly developed
• Thus, insufficient supply of O2 obtained through lungs is
supplemented through moist skin and buccal cavity.
Hearing System
• Amphibians were the first
Vertebrates to use the ear got
hearing.
• All vertebrates have an inner ear
with semicircular canals and
other structures for motion and
gravity detection.
• Tetrapods have at least one
middle ear bone for conduction of
sound waves from the tympanic
membrane (ear drum) to the inner
ear
Retinas
• Amphibian retina shows a five-layered
structure typical of the vertebrate eye.
• Amphibian “green” rods express a bluesensitive cone visual pigment
• The upper lid of the eye is fixed but the
lower one is folded into a transparent
nictitating membrane capable of moving
across the eye surface.
• Have good vision, crucial to avoid
predators and accurate movement to
capture rapidly moving prey.
Circulation
• The circulation system of amphibians
shows remarkable adaptations for a
life divided between aquatic and
terrestrial habits.
• Adults have 3 chambered heart
• Circulation to lungs and skin
separated from circulation to rest of
body; makes respiration more efficient
• Larvae have 2 chambered heart
Excretion & Osmoregulation
• Excrete ammonia or urea
• Protective covering to reduce water
loss
• No scales; smooth skin, moist with
many glands
• Skin colour due to chromatophores
located in dermis
Undergo
Metamorphosis
Their eggs lack shell and are laid
in water
Classes
• Anura: Frogs and Toads
• Caudata: Salamanders and Newts
• Gymnophiona: Caecilians
Class Anura
• Frogs and Toads
• Largest order of amphibians
• Characterised by strong hind legs for
jumping
• Lack tails in adulthood
• Smooth skin (frogs) or warty skin
(toads)
• External fertilization, with eggs laid in
water
Class Caudata
• Salamanders and Newts
• Elongated bodies with tails
• Typically have four limbs of equal size
• Capable of regenerating limbs and tails.
• Many species retain larval traits (neoteny) in
adulthood
• Internal fertilization via spermatophores.
Reptiles
• Tetrapod’s
• Bilateral
Symmetry
Reptiles
• Cold-blooded (ectothermic)
vertebrates
• Covered in dry, scaly skin that
prevents loss of water
• Breathe using lungs throughout their
lives
• Lay amniotic eggs with protective
shells or give life birth
Reptiles
• Internal Fertilization
• Strong skeletal structure adapted for
terrestrial life
• Efficient excretory system to conserve water
• Typically exhibit slow metabolism compared
to mammals and birds.
Internal
Fertilisation
• Most reptiles reproduce sexually and
have internal fertilization.
• Males have one or two penises that pass
sperm from their cloaca to the cloaca of
a female.
• Fertilization occurs within the cloaca and
fertilized eggs leave the female’s body
through the opening in the cloaca.
• In a minority of species, the eggs retained
inside the female’s body until they hatch.
An example is live birth in Boas
Strong Skeleton
• Muscles that close their jaws are attached to the
underside of the skull.
• They posses claws to help climb and cling to
branches in some reptile species.
• Limbs positioned directly beneath body rather
than side which helps to support their body on
land.
• Their bones are denser and stronger which helps
to withstand land-based movement and reduce
risk of fractures.
• Reptiles have reduced flexibility in spines which is
better suited for terrestrial locomotion.
• Reptiles perform excretion through small kidneys.
Excretory
System
• Main excretory products is uric acid.
• Reptiles lack a loop of Henle in kidneys and are not able to produce
liquid urine and so excrete in more concentrated forms.
• They have metanephric kidneys. This means they have a well-developed
glomerulus.
• Some reptiles are able to reabsorb stored water in the bladder
Life Cycle
Adaptations to the
Terrestrial Environment
• Scaly, Keratinized skin to prevent water
loss
• Lungs for respiration (no gills)
• Stronger limbs for movement on land
• Internal fertilization and direct
development
• Efficient excretory system to conserve
water
The Amniotic Egg
• Key adaptation allowing reptiles to lay
eggs on land
• Enclosed in a protective shell to
prevent desiccation
• Contains specialized membranes:
▪Amnion: Cushions embryo in fluid
▪Chorion: Facilitates gas exchange
▪Allantois: Handles waste storage
▪Yolk Sac: Provides nutrition
Orders
• Order Testudines (Turtle
and Tortoises)
• Order Squamata (Lizards
and Snakes)
• Order Crocodylia
(Crocodiles, Aligators,
Gharials)
• Order Rhynchocephalia
(Tuatara)
Order Testudines
• Turtles and Tortoises
• Hard shell for protection
• Aquatic (turtles) or terrestrial
(Tortoises)
• Long lifespans and slow metabolism
Order
Squamata
Order Crocodylia
• Crocodiles, Alligators and Gharials
• Large, semi-aquatic carnivores
• Strong jaws and powerful tails
• Parental care observed in some species
Order
Rhynchocephalia
• Tuatara
• Only one living genus
(sphenodon)
• Resemble lizards but with
distinct skull structure
• Found only in New Zealand
Topic 16: Part 1: Birds - Aves
16. BIRDS. Morphological and physiological adaptations on flight.
Endotherm.
Introduction to Birds
• Birds are among the most visible,
melodious, and diverse vertebrates, with
over 10,500 species worldwide. They
inhabit nearly every environment, from
forests and deserts to oceans and even
the poles.
• Their most distinguishing feature is
feathers, a unique characteristic that sets
them apart from all other animals.
…
• Despite millions of years of evolution, birds have
retained a highly uniform body structure adapted
for flight. Key adaptations include:
1.
Forelimbs modified into wings
2.
Hindlimbs adapted for walking, swimming, or
perching
3.
Keratinized beaks without teeth
4.
Egg-laying reproduction
• Bird anatomy is specifically designed for flight,
requiring lightweight yet strong bones, an
efficient respiratory and circulatory system, and
acute sensory abilities, particularly vision.
Origin and
Evolution of Birds
• Birds evolved from theropod dinosaurs,
as evidenced by the famous
Archaeopteryx fossil discovered in
Germany. This fossil, dated to 147
million years ago, displayed both
reptilian and avian features:
• Reptilian Traits: Bony tail, clawed
fingers, teeth in jaw sockets, and
abdominal ribs
• Avian Traits: Feathers and a furcula
(wishbone)
Birds share several anatomical and
physiological characteristics with reptiles:
1. Single occipital condyle (a skull feature)
2. Single middle ear bone (stapes)
3. Lower jaw composed of multiple bones
4. Excretion of nitrogenous waste as uric acid
5. Large, yolked eggs with surface cleavage development
Mosaic Evolution
• Birds did not evolve all their modern traits
simultaneously but gradually acquired
them. Feathers likely evolved before
flight, possibly for thermoregulation,
camouflage, or courtship displays.
Birds today are divided into:
• 1. Paleognathae (flightless birds like ostriches, kiwis)
• 2. Neognathae (flying birds with a keeled sternum for muscle
attachment)
• Flightlessness evolved independently in many bird groups,
especially on predator-free islands.
Structural and Functional Adaptations for
Flight
Birds meet strict aerodynamic requirements
for flight through unique adaptations:
1.
Feathers: provide insulation, waterproofing, and
the ability to fly.
The main types include:
• Contour feathers: Streamline the body and provide
flight surfaces
• Flight feathers: Found on wings and tail for lift and
thrust
• Down feathers: Insulation against cold
• Filoplumes: Sensory function, detecting feather
movement
Feathers develop in a sheath that later splits open,
allowing them to spread. Birds molt regularly to replace
worn-out feathers.
2. Skeletal System
Bird skeletons are lightweight yet strong due to
pneumatized bones (hollow with air spaces).
Key skeletal adaptations include:
• Fusion of bones for rigidity (synsacrum,
pygostyle)
• Large, keeled sternum for muscle
attachment
• Furcula (wishbone) stores energy during
flight
• Forelimb modifications: Fewer bones, some
fused for wing strength
3. Muscular System
Birds have large pectoralis muscles for the
downward wingstroke, which generate lift
and thrust. The supracoracoideus muscle
acts as a pulley to lift the wing during the
upstroke.
The toe-locking mechanism in perching
birds prevents them from falling off
branches while sleeping.
4. Digestive System
Birds have specialized beaks suited to their diet,
from carnivorous hawks to nectar-feeding
hummingbirds.
They lack teeth and use:
- Crop: Storage chamber in the esophagus
- Proventriculus: Secretes digestive enzymes
- Gizzard: Grinds food with swallowed pebbles
Some birds, like owls, regurgitate pellets of
indigestible material.
Flight
Mechanics
• Flight requires birds to
generate lift and thrust while
minimizing drag.
• Lift: Created by air pressure
differences above and below
the wing (Bernoulli’s
principle).
• Thrust: Generated by wing
strokes, especially primary
feathers at the wingtips.
• Drag: Reduced by
streamlined body shape and
wing adjustments.
Wing Types
• Birds have different wing designs for specific
flight needs:
1.
Elliptical Wings (e.g., sparrows, woodpeckers)
– Good for maneuvering in forests.
2.
High-Speed Wings (e.g., swallows, falcons) –
Designed for sustained fast flight.
3.
Active Soaring Wings (e.g., albatrosses) –
Long, narrow wings ideal for ocean gliding.
4.
Passive Soaring Wings (e.g., hawks, vultures)
– Broad wings with slots to capture rising
warm air.
• Hummingbirds have a unique sculling motion
that allows them to hover in place.
Migration and Navigation
•
Migration allows birds to access seasonal food resources, avoid predators,
and breed in optimal conditions.
•
Migration Patterns
•
Most birds migrate north in summer and south in winter.
•
Arctic Terns travel over 18,000 km between the Arctic and Antarctica.
•
Bar-tailed Godwits fly 11,000 km non-stop from Alaska to New Zealand.
Navigation Methods
•
Landmarks such as rivers and coastlines
•
Sun and star positioning
•
Earth’s magnetic field, detected through magnetite deposits in their beaks
•
Internal clocks to adjust for time zone shifts
Mating Systems and
Parental Care
Birds exhibit diverse mating strategies,
including:
• Monogamy (one mate per season, e.g.,
swans)
• Polygamy (multiple mates, e.g., peacocks)
• Polygyny (one male, multiple females)
• Polyandry (one female, multiple males)
Parental care varies widely, from precocial
young (born active, e.g., ducks) to altricial
young (born helpless, e.g., songbirds).
Human Impact on Bird Populations
Bird populations are declining due to:
• Habitat destruction (deforestation, urbanization)
• Climate change (altered migration patterns, food shortages)
• Pollution (pesticides, plastic waste)
• Hunting and poaching (illegal trade, sport hunting)
• Efforts to conserve birds include protected areas, migration
corridors, and banning harmful pesticides like DDT (which nearly
wiped out bald eagles).
Conclusion
• Birds are highly specialized vertebrates with adaptations for flight,
migration, and survival in diverse environments. Their evolutionary
link to dinosaurs, unique physiological systems, and intricate
behaviors make them a fascinating subject of study. However,
conservation efforts are necessary to protect many species from
human-induced threats.
Topic 16: Part 2: Mammals
MAMMALS. General characteristics. Tegument and derivatives.
Patterns of feeding and dental formulas. Diversity
Origin and Evolution
of Mammals
Mammals evo lved from synapsid amniotes, specifically a lin eage kn own as therapsids, dur ing the Paleozo ic E ra.
These early ancestor s sh owed ev olutionary traits that wo uld later define mammals, such as:
•
A h igh metabo lic rate
•
A mo re advanced jaw structur e for stronger bites
•
Heterodon t teeth (different typ es of teeth for specialized feedin g)
•
A secondary p alate, allowing breath ing while eating
•
Turbinate bo nes in the nasal cavity , aiding in heat reten tion
The cy nodonts, a subgroup of therapsids, surviv ed into the Mesozoic Era and d evelop ed addition al mammalian traits, includinga
diap hragm for efficient breath ing and th e loss of lumb ar ribs, increasing spin al flexibility .
Du ring th e Triassic period, th e fir st mammals appeared, evolving fr om small, shrew-like creatures. These ear ly mammals had:
•
Diphyodo nt teeth (teeth that are rep laced only once in a lifetime)
•
A fully for med secondar y palate
•
Three middle ear bones (malleus, in cu s, and stapes), impr oving hearing
•
Lactation and paren tal care, key traits of mo dern mammals
Mammals remained small and no ctu rnal du ring th e age of dinosaurs, only diver sifyin g significantly after the Cretaceou s-Paleogene
mass extinctio n. The Ceno zoic Era saw an explosion of mammalian diversity, leading to modern ord ers such as primates, r odents,
carniv ores, and cetaceans (whales, do lphins, and porp oises) .
Structural and Functional Adaptations of Mammals
Mammals are endothermic vertebrates with adaptations that
allow them to survive in diverse environments, from deserts to
the deep ocean.
Key Mammalian Characteristics
• Hair: Provides insulation, protection, and sensory functions
• Mammary glands: Nourish offspring with milk
• Middle ear bones: Improve hearing sensitivity
• Diaphragm: Enhances breathing efficiency
• Heterodont dentition: Allows diverse diets
• Placental nourishment: In most species, embryos develop
inside the uterus
Skin and Hair
Mammalian skin contains a variety of glands:
1.
Sweat glands (for temperature
regulation)
2.
Sebaceous glands (secrete oils to
condition skin and hair)
3.
Scent glands (used for communication
and marking territory)
Hair plays a crucial role in insulation and
camouflage, while some mammals (such as
aquatic species) have reduced or lost it
Mammalian Teeth and
Feeding Adaptations
•
Mammals have specialized heterodont teeth, categorized as:
1. Incisors (for cutting)
2. Canines (for tearing)
3. Premolars and molars (for grinding)
•
Different dietary adaptations include:
•
Insectivores (shrews, anteaters): Pointed teeth for piercing exoskeletons
•
Herbivores (deer, cows, rodents): Broad molars for grinding plants
•
Carnivores (lions, wolves): Sharp canines and carnassial teeth for shearing meat
•
Omnivores (bears, humans): Versatile teeth for a mixed diet
Some herbivores have specialized digestive systems, such as ruminants (cows,
sheep) with four-chambered stomachs for fermenting plant material .
Mammalian Locomotion and
Environmental Adaptations
Mammals exhibit a variety of locomotor
adaptations, including:
1.
Cursorial locomotion (running, e.g.,
cheetahs, horses)
2.
Saltatorial locomotion (jumping, e.g.,
kangaroos, rabbits)
3.
Arboreal locomotion (climbing, e.g.,
primates)
4.
Aquatic locomotion (swimming, e.g.,
whales, dolphins)
5.
Fossorial locomotion (burrowing, e.g.,
moles)
Hibernation and
Migration
Many mammals have evolved strategies to
cope with seasonal changes:
- Hibernation: A deep metabolic depression
(e.g., bears, ground squirrels)
- Torpor: A short-term decrease in metabolism
(e.g., bats)
- Migration: Long-distance seasonal
movement (e.g., caribou, whales)
Reproductive Strategies of Mammals
Mammals reproduce sexually, with internal fertilization. They are classified into three reproductive groups:
1. Monotremes (egg-laying mammals)
•
• Examples: Platypus, echidna
•
• Lay eggs, but nourish young with milk
•
• Found only in Australia and New Guinea
2. Marsupials (pouched mammals)
•
• Examples: Kangaroos, opossums
•
• Give birth to underdeveloped young, which crawl into the mother’s pouch for further development
3. Placentals (eutherians)
•
• Examples: Humans, elephants, whales
•
• Develop in a uterus with a placenta, allowing longer gestation and greater fetal development
Mammalian parental care is highly developed, with extended nurturing periods that help offspring learn
survival skills.
Mammalian Evolution
and Human Origins
Human Evolution: Humans belong to the order Primates, which
includes lemurs, monkeys, and apes. Fossil evidence suggests
Homo sapiens originated in Africa about 200,000 years ago.
Key evolutionary changes in primates include:
- Bipedal locomotion (walking upright)
- Larger brain size (enhancing problem-solving and
communication)
- Tool use and culture (developed uniquely in humans)
The Neanderthals (Homo neanderthalensis) coexisted with early
modern humans but went extinct about 39,000 years ago .
Mammalian Diversity
and Conservation
Mammals occupy nearly every habitat, with over 5,700 species
classified into three major groups:
• Monotremata (egg-laying mammals)
• Metatheria (marsupials)
• Eutheria (placental mammals)
Major mammalian orders include:
• Rodentia (rats, mice, squirrels) – The most diverse group
• Carnivora (cats, dogs, bears) – Predators with sharp teeth
• Cetacea (whales, dolphins) – Fully aquatic mammals
• Primates (monkeys, apes, humans) – Intelligent, social
mammals
Threats to Mammals
Mammalian species are threatened by:
1. Habitat destruction (deforestation, urbanization)
2. Climate change (rising temperatures affecting migration and
food sources)
3. Poaching and illegal wildlife trade (e.g., elephants for ivory, tigers
for skins)
4. Pollution (plastic waste, chemical contaminants)
Conservation efforts focus on protected areas, captive breeding,
and anti-poaching laws .
Conclusion
Mammals are an incredibly diverse and adaptable group, ranging
from tiny bats to massive whales. Their evolutionary success is
due to specialized adaptations in metabolism, reproduction, and
behavior. However, human activities pose significant threats,
making conservation critical for their survival.
References
• Integrated Principles of Zoology