Animal Diversity I
Reproduction and Development
 Most animals reproduce sexually, with the
diploid stage usually dominating the life cycle
 After a sperm fertilizes an egg, the zygote
undergoes rapid cell division called cleavage
 Cleavage leads to formation of a blastula
 The blastula undergoes gastrulation, forming
a gastrula with different layers of embryonic
tissues
After fertilization, embryonic development proceeds through
cleavage, gastrulation, and organogenesis
 Important events regulating development occur
during fertilization and the three stages of embryonic
development that build the animal’s body
1. Cleavage: cell division creates a hollow ball of
cells called a blastula
2. Gastrulation: cells are rearranged into a threelayered gastrula
3. Organogenesis: the three layers interact and
move to give rise to organs
CLEAVAGE
 Fertilization is followed by
cleavage, a period of rapid
cell division without growth
 Cleavage partitions the
cytoplasm of one large cell
into many smaller cells
called blastomeres
 The blastula is a ball of
cells with a fluid-filled
cavity called a blastocoel
Fig. 47-6
Morula
a "mulberry" appearance
Blastocoelic
cavity ;
Precursor of
the Coelomic
cavity.
Blastocoel
(a) Fertilized egg
(b) Four-cell stage
(c) Early blastula
http://www.ceoe.udel.edu/
Antarctica/devo.html
For sea urchin embryo
development / cleavage
Gastrula
(d) Later blastula
From Oocyte to Blastocyst: Human Early Embryogenesis
4 Cell Human Embryo:
during each mitotic
division the embryo does
not increase in size and
divides the existing
cytoplasm.
D2 - (day 2) 4-cell
human embryo
Human Embryo (day 3)
morula
Human Embryo (day 5)
blastocyst
Morula: (Latin, morula = mulberry) An early stage in post-fertilization development when cells have rapidly divided
to produce a solid mass of cells (12-15 cells) with a "mulberry" appearance. This stage is followed by formation of a
cavity in this cellular mass (blastocyst stage). In humans, morula stage of development occurs during the first week
following fertilization.
http://php.med.unsw.edu.au/embryology/index.php?title=2010_BGD_Practical_3_-_Early_Cell_Division
The following figure is from a recent study[2] using video and genetic analysis of in vitro human
development during week 1 following fertilization.
KIND OF EGGS:
 The eggs and zygotes of
many animals, except
mammals, have a definite
polarity
 The polarity is defined by
distribution of yolk
(stored nutrients)
 The vegetal pole has more
yolk; the animal pole has
less yolk
Fig. 32-2-1
Cleavage
Zygote
Eight-cell stage
Fig. 32-2-2
Cleavage
Zygote
Cleavage Blastula
Eight-cell stage
Blastocoel
Cross section
of blastula
Fig. 32-2-3
Blastocoel
Cleavage
Endoderm
Cleavage Blastula
Ectoderm
Zygote
Eight-cell stage
Gastrulation
Blastocoel
Archenteron
Gastrula
Blastopore
Cross section
of blastula
ZEBRA FISH DEVELOPMENT
http://www.exploratorium.edu/imaging_station/gallery.php?Category=Zebrafish&Section=Introduction
 Many animals have at least one larval stage
 A larva is sexually immature and
morphologically distinct from the adult; it
eventually undergoes metamorphosis
Free swimming Sea
urchin larva
Body Plans: Symmetry
Animals can be characterized by “body plans”
• Zoologists sometimes categorize animals according
to a body plan, a set of morphological and
developmental traits
• A grade is a group whose members share key
biological features
• A grade is not necessarily a clade, or monophyletic
group
 All animals, and only animals, have Hox genes
that regulate the development of body form
 Although the Hox family of genes has been
highly conserved, it can produce a wide diversity
of animal morphology
 The GASTRULA gives rise to:
 Body symmetry
 Germ layers
Symmetry
 Animals can be categorized according to the
symmetry of their bodies, or lack of it
 Some animals have radial symmetry
Fig. 32-7
(a) Radial symmetry
(b) Bilateral symmetry
 Two-sided symmetry is called bilateral symmetry
 Bilaterally symmetrical animals have:
 A dorsal (top) side and a ventral (bottom) side
 A right and left side
 Anterior (head) and posterior (tail) ends
 Cephalization, the development of a head
Tissues
• Animal body plans also vary according to the
organization of the animal’s tissues
• Tissues are collections of specialized cells
isolated from other tissues by membranous
layers
• During development, three germ layers give
rise to the tissues and organs of the animal
embryo
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
•
Ectoderm is the germ layer covering the embryo’s surface
•
Endoderm is the innermost germ layer and lines the
developing digestive tube, called the archenteron
•
the mesoderm is one of the three primary germ cell layers
- the other two are the ectoderm and endoderm - in the
very early embryo. The mesoderm is the middle layer. It
differentiates to give rise to a number of tissues and
structures including bone, cartilage, muscle, connective
tissue (including that of the dermis), blood vascular,
reproductive, excretory and urinogenital systems and
contributes to some glands.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Germ layers: Tissues/organs
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Teratoma : Tumor of 3 germ layers
•
ATumor derived from the three germ layers, are
thought to be present at birth (congenital).
•
‘Teratoma’, derived from the Greek word for
‘monster’, is a type of tumor that can grow teeth
& hair, as pictured.
•
A teratoma is an encapsulated tumor.
•
Sometimes the capsule encompasses one or
more fluid-filled cysts and when a large cyst
occurs there is a potential for the teratoma to
produce a structure within the cyst that
resembles a fetus.
•
In part because it is encapsulated, a teratoma
usually is benign, although several forms of
malignant teratoma are known and some of these
are common.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Diploblastic animals have
ectoderm and endoderm
The only diploblastic animals are cnidaria and ctenophores (corals,
jellyfish and comb jellies), and the only monoblastic animals are porifera
(sponges).
Triploblastic animals also
have an intervening
mesoderm layer; these
include all bilaterians.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Germ layers: Tissues/organs
 Ectoderm is the germ layer covering the embryo’s
surface
 Endoderm is the innermost germ layer and lines
the developing digestive tube, called the
archenteron
 Diploblastic animals have ectoderm and endoderm
 Triploblastic animals also have an intervening
mesoderm layer; these include all bilaterians
1.
Monoblastic: Simpler animals, such as sea sponges have one germ
layer and lack true tissue organisation.
2.
Diploblastic animals have ectoderm and endoderm
Diploblastic organisms are organisms which develop from such a blastula,
and include cnidaria
•
The endoderm allows them to develop true tissue. This includes tissue
associated with the gut and associated glands. The ectoderm on the
other hand gives rise to the epidermis, the nervous tissue, and if
present, nephridia.
3. Triploblastic animals also have an intervening mesoderm layer; these
include all bilaterians. All the more complex animals (from flat worms
to humans) are triploblastic with three germ layers (a mesoderm as well
as ectoderm and endoderm). The mesoderm allows them to develop
true organs.
Body Cavities
 Most triploblastic animals possess a body
cavity
 A true body cavity is called a coelom and
is derived from mesoderm.
 Coelomates are animals that possess a
true coelom
Fig. 32-8
Coelom
Earthworm
Digestive tract
(from endoderm)
Body covering
(from ectoderm)
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
(a) Coelomate
Body covering
(from ectoderm)
Ascaris / Tape worm
Pseudocoelom
Muscle layer
(from
mesoderm)
Digestive tract
(from endoderm)
(b) Pseudocoelomate
Body covering
(from ectoderm)
Planaria
Tissuefilled region
(from
mesoderm)
Wall of digestive cavity
(from endoderm)
(c) Acoelomate
Fig. 32-8a
I. Coelomate / Eucelomic
Coelom
Digestive tract
(from endoderm)
Body covering
(from ectoderm)
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
Celomic Cavity: Location and Structural Plan
 Peritoneal / celomic cavity
 Lubricates digestive organs
 Allows them to slide across
one another
 Peritoneum – mesodermderived serous membrane of the
abdominal cavity
 Visceral – covers external
surface of most digestive
organs
 Parietal – lines the body wall
II. Pseudocoelomates
 A pseudocoelom is a body cavity derived from
the mesoderm and endoderm
 Triploblastic animals that possess a
pseudocoelom are called pseudocoelomates
All the organs (digestive & reproductive)
“spill out” when the animal is dissected.
Fig. 32-8b
Body covering
(from ectoderm)
Pseudocoelom
Digestive tract
(from endoderm)
(b) Pseudocoelomate
Muscle layer
(from
mesoderm)
III. Acoelomates: Tripoblastic animals that lack body cavity
Body covering
(from ectoderm)
Tissuefilled region
(from
mesoderm)
Wall of digestive cavity
(from endoderm)
(c) Acoelomate
Protostome and Deuterostome Development
 Based on early development, many animals
can be categorized as having:
 Protostome development or
 Deuterostome development
Fig. 32-9
Protostome development
(examples: molluscs,
annelids)
Deuterostome development
(examples: echinoderm,
chordates)
Eight-cell stage
Eight-cell stage
Spiral and determinate
Radial and indeterminate
(a) Cleavage
(b) Coelom formation
Key
Coelom
Ectoderm
Mesoderm
Endoderm
Archenteron
Coelom
Mesoderm
Blastopore
Blastopore
Solid masses of mesoderm
split and form coelom.
Mesoderm
Folds of archenteron
form coelom.
Anus
Mouth
(c) Fate of the blastopore
Digestive tube
Mouth
Mouth develops from blastopore.
Anus
Anus develops from blastopore.
Fig. 32-9a
Deu = Anu
Protostome development
(examples: molluscs,
annelids)
Deuterostome development
(examples: echinoderms,
chordates)
Eight-cell stage
Eight-cell stage
Spiral and determinate
Radial and indeterminate
(a) Cleavage
Coelom Formation
 In protostome development, the splitting of solid
masses of mesoderm forms the coelom
 In deuterostome development, the mesoderm
buds from the wall of the archenteron to form
the coelom
Fig. 32-9b
Protostome development
(examples: molluscs,
annelids)
Deuterostome development
(examples: echinoderms,
chordates)
(b) Coelom formation
Coelom
Key
Ectoderm
Mesoderm
Endoderm
Archenteron
Coelom
Mesoderm
Blastopore
Solid masses of mesoderm
split and form coelom.
Blastopore
Mesoderm
Folds of archenteron
form coelom.
Fate of the Blastopore
 The blastopore forms during gastrulation and
connects the archenteron to the exterior of the
gastrula.
 In protostome development, the blastopore becomes
the mouth
 In deuterostome development, the blastopore
becomes the anus
Fig. 32-9c
Protostome development
(examples: molluscs,
annelids)
Deuterostome development
(examples: echinoderms,
chordates)
Anus
Mouth
(c) Fate of the blastopore
Key
Digestive tube
Anus
Mouth
Mouth develops from blastopore. Anus develops from blastopore.
Ectoderm
Mesoderm
Endoderm
Fig. 32-3
The common ancestor of living animals may have lived between 675 and 875 million
years ago.
This ancestor may have resembled modern choanoflagellates, protists that are the closest
living relatives of animals.
Individual
choanoflagellate
Choanoflagellates
OTHER
EUKARYOTES
Sponges
Animals
Collar cell
(choanocyte)
Other animals
Neoproterozoic Era (1 Billion–524 Million Years Ago)
 Early members of the animal fossil record include the
Ediacaran biota, which dates from 565 to 550 million years
ago.
 First discovered in the Ediacara Hills of Australia
 First macroscopic fossils of animals
 Soft bodied organisms: sponges, cnidarians
SPECIMES FOR
DISSECTION
Sponges: Phylum Prorifera
Scypyha (Grantia)
Sponges: Phylum Prorifera
 Sponges are the simplest animals anatomically, lacking many of the features that
characterize all other animals. However, close studies of both their embryology and their
genomes show that sponges are closely related to other animals, and not to any other
kingdom.
 The apparent simplicity has led biologists to regard sponges as primitive offshoots of the
animal lineage, having split off before the evolution of the more complex features that
most other animals share. However, some studies have suggested that the ancestors of
sponges may actually have been more complex.
 All sponges live in the water; most live in the ocean.
Sponge features:
No true tissues. Although sponges have several types of cells, the cells do not show the level of
tissue organization seen in other animals.
 No symmetry. Other animals show radial symmetry (cnidarians, for example) or bilateral
symmetry (humans). Sponges have variable and irregular body forms.
 Intracellular digestion. Unlike other animals, sponge cells take in small food particles by
phagocytosis.
 Spicules: hard, crystalline structures secreted outside the cells; see the description below

Sponges: Phylum Prorifera

Porifera
The sponges, a phylum of the animal kingdom which includes about 5000 described
species.

The body plan of sponges is unique among animals. Currents of water are drawn
through small pores, or ostia, in the sponge body and leave by way of larger openings
called oscula.

The beating of flagella on collar cells or choanocytes, localized in chambers on the
interior of the sponge, maintains the water current.

Support for the sponge tissues is provided by calcareous or siliceous spicules, or by
organic fibers, or by a combination of organic fibers and siliceous spicules. Some species
have a compound skeleton of organic fibers, siliceous spicules, and a basal mass of
aragonite or calcite.

The skeletons of species with supporting networks of organic fibers have long been used
for bathing and cleaning purposes.
Because of their primitive organization, sponges are of interest to zoologists as an aid in
understanding the origin of multicellular animals
Sponges: Scypha
 Scypha (Grantia)
 Scypha is a small, tube-shaped sponge. We
have two microscope slides of Scypha: a
cross section and a longitudinal section.
 Cross section:
 Scypha uses the flagella on its
choanocytes to draw water through its
body so it can capture small suspended
particles of food. The water is drawn in
through the incurrent canals, passes
through the radial canals, and finally out
through the spongocoel.
 The spongocoel is an empty space in the
middle of the body. It is not comparable to
the coelom of other animals, because there
are no organs in it; it's just an empty tube
through which water is expelled.
 Longitudinal section:
 At higher magnification, you will be
able to make out several types of
cells. The choanocytes, or collar
cells, perform the essential
functions of pumping water by
flagellar action and capturing food
particles with their collar of
microvilli. The incurrent and radial
canals are lined with choanocytes.
 Amoebocytes are cells with an
amoeboid, or irregular, shape. They
perform various functions and can
differentiate to become other cell
types. The amoebocytes are
surrounded by a layer of extracellular
matrix material called mesohyl.
 Pinacocytes are flattened cells that
form the outer layer of the sponge.
Fire sponge injury:
August 2010 at key Biscayne
Tedania ignis (Fire Sponge)
 The spicules are sharp, crystalline
structures made of calcium carbonate,
the same material that makes up the
shells of many other marine animals.



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The spicules reinforce the body and
make it more resistant to attack by other
animals.
Leucosolenia is a calcareous sponge;
some other sponges have spicules made
of silicon dioxide, the main component
of glass.
At higher magnification, the spicules
are clearly visible (and, incidentally,
rather beautiful). In order to see them
clearly, you may need to adjust the
condenser on your microscope (the
wheel just under the stage).
Calcium carbonate is formed by many
marine animals. However, it also
dissolves fairly easily if the water's pH
decreases even slightly (acid);
Wash injuries with vinegar !
Phylum Cnidaria
HYDRA
Commonly known as anemones, jellyfish or corals, they play important ecological roles in food webs.
Phylum Cnidaria

Phylum Synopsis:
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About 10,000 species of cnidarians (formerly called coelenterates) are animals with true tissues and are consequently placed in the
Eumetazoa branch of the animal kingdom: a fact supported by modern molecular studies.
Body construction is simple and is only a few cells thick with an outer epidermis and inner gastrodermis sandwiching a gel like
substance called mesoglea in which a few amoeboid cells migrate about.
Consequently, cnidarians are described as diploblastic (2 layers) in contrast to the other animals you will study which are said to be
triploblastic.
Cnidarians have radial symmetry and only rudimentary organs.
All are aquatic and are found in both fresh and salt water .
Commonly known as anemones, jellyfish or corals, they play important ecological roles in food webs.
The life cycles of many, but certainly not all species, include alternate generations with two different body forms: a sedentary polyp
and a free-swimming medusa.
A unique cell type, the cnidocyte, is found in all species and is used in gathering food.
Food is taken into a central gastrovascular cavity, often with branches into the tentacles.
Digestion is extracelluar followed by intracellular absorption of nutrients.
The branches of the gastrovascular cavity allow food particles to travel to remote parts of the body and therefore serve a rudimentary
circulatory system function.
A rudimentary nervous system and simple muscle cells allow the animals to move and to react to their environments.
Specialized organs for respiration, circulation and excretion are lacking.
The skeleton may be external as in corals or hydrostatic as in anemones.
Gonads develop during breeding seasons with sexes usually separate.
Asexual reproduction is common, usually by fragmentation.
Phylum Cnidaria contains three taxonomic classes:

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Hydrozoa,
Scyphozoa
Anthozoa.
Example: HYDRA
Phylum Cinidaria
Class Hydrozoa: Sessile living Hydra
OBSERVING LIVE HYDRA

Place a living Hydra in a small dish of water
and examine with the dissecting
microscope. At the upper end of the animal,
observe several elongate, actively moving
tentacles, which are used to capture food
(Figure 3). At the centre of this circle of
tentacles, is the mouth. Tap the edge of your
dish and observe the extreme contractility of
this organism.

To observe your specimen ingesting food,
add several Daphnia (or other available food
organisms) to your dish and observe with the
dissecting microscope. When the tentacles of
the Hydra come into contact with its prey,
the prey jerk for several minutes before
becoming still.

The food organism reacts in this way because
it is being stung by numerous wart-like
nematocysts on the tentacles. Once the food
organism has been ingested, it will be
degraded within the gastrovascular cavity
and the small particles engulfed by the
gastrodermal cells by phagocytosis.
Phylum Cnidaria
Class Hydrozoa : HYDRA
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Being small, exclusively aquatic organisms cnidarians require
neither a special respiratory nor circulatory system. The
entire body surface can participate in gas exchange since all
cells in these diploblastic (two-layered) animals are
constantly moist and exposed to the gas-containing medium.
In addition, no cell is ever far enough from the source of
either nutrient materials or gases to necessitate any more
elaborate transport than either direct diffusion from cell to
cell or diffusion through the very watery mesoglea that exists
between the two cell layers (the epidermis and the
gastrodermis).
Hydra reproduce asexually by simple budding and sexually by
the production of sperm and ova. Budding consists of a
simple outgrowth from the body wall. The gastrovascular
cavity of the bud is initially continuous with that of the
parent. The bud will separate from the parent at maturity.
Examine slides; observe Hydra budding.
The gametes for sexual reproduction are produced in organs
called spermaries (testes) and ovaries, which are
protuberances along the body wall (Figure 3). Both sex
organs may be present in a single organism or in two separate
organisms.
Examine slides and try to locate these gamete-producing
organs, and the nematocysts.
Nematocyst
See the hair-like trigger in
the nematocyst .
http://knight.noblehs.sad60.k12.me.us/content/exploringLife/text/chapter23/concept23.3.html
“Immortal" Jellyfish Swarm World's Oceans
National Geographic: 10/28/2010
Immortal" Jellyfish Swarm World's Oceans
Ker Than
for National Geographic News
January 29, 2009
A potentially "immortal" jellyfish species that can age backward—the Benjamin Button of the
deep—is silently invading the world's oceans, swarm by swarm, a recent study says.
Like the Brad Pitt movie character, the immortal jellyfish transforms from an adult back into a
baby, but with an added bonus: Unlike Benjamin Button, the jellyfish can do it over and over
again—though apparently only as an emergency measure.
RELATED
•Mysterious Jellyfish Swarms Seen in Europe, U.S. (August 11, 2008)
•ictures of Jellyfish and Other Translucent Creatures
•PHOTO: Blue Jellyfish Swarm Australia Beaches (January 7, 2007)
About as wide as a human pinky nail when fully grown, the immortal jellyfish (scientific name:
Turritopsis dohrnii) was discovered in the Mediterranean Sea in 1883. But its unique ability was
not discovered until the 1990s.
How the Jellyfish Becomes "Immortal"
Turritopsis typically reproduces the old-fashioned way, by the meeting of free-floating sperm and
eggs. And most of the time they die the old-fashioned way too.
But when starvation, physical damage, or other crises arise, "instead of sure death, [Turritopsis]
transforms all of its existing cells into a younger state," said study author Maria Pia Miglietta, a
researcher at Pennsylvania State University.
The jellyfish turns itself into a bloblike cyst, which then develops into a polyp colony, essentially
the first stage in jellyfish life.
The jellyfish's cells are often completely transformed in the process. Muscle cells can become
nerve cells or even sperm or eggs.
Through asexual reproduction, the resulting polyp colony can spawn hundreds of genetically
identical jellyfish—near perfect copies of the original adult.
This unique approach to hardship may be helping Turritopsis swarms spread throughout the
world's oceans, she added.
(Related picture: giant jellyfish swarm Japan.)
Phylum Platyhelminthes
Class Turbellaria: Free living flatworms such as Planaria
Flatworms are the simplest bilateral animals.
PLANARIA
Phylum Platyhelminthes
Class Turbellaria: Free living flatworms such as Planaria
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Phylum Platyhelminthes Phylum Trend Synopsis: Commonly called flatworms, the phylum name is derived from
Greek and describes the body shape of these animals: dorsally ventrally flattened but otherwise worm-like.
The approximately 20,000 species are classified into four classes: the free living flatworms in the Class Turbellaria, the
parasitic monogeans in the Class Monogea, the parasitic flukes in the the Class Trematoda, and the parasitic
tapeworms in the Class Cestoidea.
The body plan is that of an elongated organism that is dorsally ventrally flattened with bilateral symmetry and with a
hint of cephalization. Distinct tissues and organ systems are found, but the organs are not located in a body cavity.
Cross sections of these animals show that, except for the digestive cavity, no other internal cavity is found. Because the
organs are in direct contact with a surrounding loosely organized tissue, these animals are said to be acoelomate.
These animals are said to be triplpoblastic because three layers of cells can be seen: an outer epidermis (ectoderm), a
middle layer that may be several cells thick (mesoderm)and a distinct lining of the gut the endoderm. The digestive
system is described as incomplete because it is not a tube with a mouth at one end and anus at the other. There is only
one opening, so it is described asa sac-like system. Food enters the mouth and is digested in a branched
gastrovascular cavity. Any non-digestable residue must be regurgitated back through the mouth.
Muscle layers are well developed and controlled by a distinct nervous system with two longitudinal nerve cords that run
the length of the body. Two nerve ganglia and sensory receptors at the anterior end coordinate activity sending nerve
signals to the rest of the body by two ventral longitudinal nerve cords. There is no separate skeletal system and body
support is by hydrostatic pressure or by a cuticle. There are no special organs for respiration and circulation. Diffusion
across the body surface or from the gastrovascular cavity to the body cells fulfills these functional needs.
Individuals may have both male and female sex organs, producing sperm and eggs. Fertilization is internal. Microscopic
fertilized eggs are released. Development may be direct into minature adult forms or indirect through a indepemdent
larval stage.
As parasites of animals, the platyhelminthes have substantial impacts on ecosystems.
Modern analysis of DNA sequences indicates that these animals may be related to the protostome branch of the animal
phylogentic tree.
Planarians have three tissue layers (shown
above) and are bilaterally symmetrical.
Bilaterally symmetrical objects can be
divided into identical right and left halves,
like a shovel.
Plan aria Regeneration video:
http://www.exploratorium.edu/imaging_station
/research/planaria/story_planaria1.php
 Planaria can harm shrimp and
their offspring.
 If your shrimplets always
disappear after a few days, planaria
may be the reason.
 They even attack full grown
shrimp: The tiger shrimp showed
on the pics below was jumping like
crazy trough the tank.
 A closer look showed that a
planaria had been creeping inside
the body. The shrimp died later
on.
Tiger shrimp attacked by planaria, died later on
http://www.blue-tiger-shrimp.com/blog/category/diseases-and-problems/planaria-parasites/
Phylum Nematoda
Free living and Parasitic: e.g roundworm such as Ascaris
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Phylum Synopsis:
The 90,000 species of roundworms are remarkably similar; all have cylidrical, non-segmented bodies that are bilaterally
symmetrical and covered by a tough proteinaceous exoskeleton called a cuticle.
Body size is from less than 1 mm to more than 1 meter in length.The internal organs are free in a body cavity called a
pseudocoel.
They have a complete digestive tract running as a tube from the mouth to the anus.
Body wall muscles are well developed but run only longitudinally along the body, not circularly around the body. This
allows them only to thrash from side to side but not to extend forward as other worms do.
They have a nervous system that coordinates movement but shows little cepahalization. Sense organs are not
prominent. An excretory system is present.
Nematodes lack a distinct circulatory and respiratory system. Circulation occurs when fluids in the body cavity slosh
back and forth in the pseudocoel.
Respiration occurs by diffusion of gases across the cuticle. Sexes are usually separate and internal fertilization results
from mating. Development is direct to minature forms of the adults.
The cuticle is shed to allow growth.
Nematodes are found in aquatic habitats, moist soils, and as internal parasites of plants and animals. They play
important ecological roles as decomposers of detritus and as parasites.
Modern molecular evidence (DNA sequence analysis) has lead to a hypothesis that nematodes may be regressive
protostomes related to arthropods and together the two phyla are grouped in clade called Ecdysozoa, a term that reflects
a common characterisitc of shedding the cuticle during growth periods.
Adult worms (1) live in the lumen of the small intestine.
A female may produce approximately 200,000 eggs per day, which
are passed with the feces (2). Unfertilized eggs may be ingested but
are not infective. Fertile eggs embryonate and become infective
after 18 days to several weeks (3), depending on the environmental
conditions (optimum: moist, warm, shaded soil). After infective
eggs are swallowed (4), the larvae hatch (5), invade the intestinal
mucosa, and are carried via the portal, then systemic circulation
and/or lymphatics to the lungs . The larvae mature further in the
lungs (6) (10 to 14 days), penetrate the alveolar walls, ascend the
bronchial tree to the throat, and are swallowed (7). Upon reaching
the small intestine, they develop into adult worms (8). Between 2
and 3 months are required from ingestion of the infective eggs to
oviposition by the adult female. Adult worms can live 1 to 2 years.
Ascaris : Male
See the “hook” in the tail end; only present in males
Female Ascaris
Uterine horns
Intestine: Flat, ribbon-like,
running the length of the animal
Female Ascaris
Vagina
Uterine horns
Female Ascaris: Cross Section
Female Ascaris: Cross Section
F
G
I
A
D
C
C
Uterus full
of eggs ! !
B
Ascaris: Female
Phylum Annelida: Segmented worms
Example: Earthworm
 Annelid worms are quite different from flatworms or nematodes. Having a segmented
body with a true coelom makes them considerably more complex in their structure and
their movements.
 Annelid features:
 Three tissue layers in embryo. Almost all animals share this basic feature; the sponges
and cnidarians are exceptions.
 Segmented body. Contrast this with nematodes, which have unsegmented bodies.
 True coelom: The coelom of an annelid is a large space in which the internal organs form.
Since the body is segmented, the coelom is segmented, too.
 Complete digestive tract: The digestive tract run througout the length of the body, and
different regions show a significant degree of specialization (unlike flatworms or
nematodes).
 Closed circulatory system: Blood is contained within the circulatory system. This is
particularly important given that the segmented body prevents coelomic fluid from
cirulating througout the body (as it does in nematodes).
Earthworms (class Oligochaeta)
Mating
Earthworms are simultaneous hermaphrodites -- each individual
produces both eggs and sperm at the same time. When a pair of
earthworms mates, each individual gives sperm to the other. Sperm is
released through a male genital pore and received by the female
genital pore on the other individual.
Crop
Hearts
Gizzard
Seminal Vesicles
Testis; they are round, as
opposed to the seminal
vesicles, that are elongated
and bigger
Seminiferous tubes
Intestine
Circulatory System
Septa
Nephridia
http://www.biology.iastate.edu/Courses/211L/Nemato/Ascarindx.htm
http://knight.noble-hs.sad60.k12.me.us/content/exploringLife/text/chapter23/concept23.3.html
http://www.deanza.edu/faculty/mccauley/6a-labs-sponges-01.htm
http://accessscience.com/abstract.aspx?id=102500&referURL=http%3a%2f%2f
accessscience.com%2fcontent.aspx%3fid%3d102500
http://kentsimmons.uwinnipeg.ca/16cm05/16labman05/lb5pg3.htm