Animal Kingdom
Sponges to Mammals
What is an Animal?
• Animal characteristics:
– Multicellular
– Eukaryotes
• Cells with nuclei and membrane bound organelles
– Cells lack cell walls
– Cells of most animals are organized into tissues
• Ex: epithelial, connective, nervous, etc.
Invertebrates vs. Vertebarates
• Majority ~95% of animals are invertebrates
– Lack backbone or vertebral column
• Insects, worms, snails, octopi
• Remaining 5% are vertebrates
– Have a backbone
• Fishes, amphibians, reptiles, birds, and mammals
Animal Functions
Functions for survival:
• Feeding- via ingestion
• Respiration- all take in O2 and eliminate CO2
• Circulation- simple diffusion or complex circulatory
systems
• Excretion- elimination of waste, primarily ammonia
• Response- nerve cells and receptor cells
• Movement- few sessile adults, most motile
– Use muscles or muscle-like tissues
• Reproduction- most sexually using haploid gametes
– Some inverts by asexual means
• Many functions regulated by feedback inhibition- the
product stops or limits the process
– Ex: insulin and blood glucose levels
• Complex animals have
-high levels of cell specialization
-internal body organization
-bilateral symmetry
-front end or head with sensory organs and body cavity
-embryos develop in layers
Patterns of Development
Protostomes vs. Deuterostomes
• Embryonic development:
– Zygote (fertilized egg) undergoes a series of
divisions to become a blastula (ball of cells)
– Blastula folds in on itself to form a single opening
called a blastopore
• Blastopore leads into a central tube that
becomes the digestive tract, but differs in
protostomes and deuterostomes
– Protostome- blastopore becomes mouth
– Deuterostome- blastopore becomes anus
Embryonic Germ Layers
• Most animal embryos differentiate into 3
layers called germ layers
– Endoderm- innermost germ layer
• Becomes digestive tract and much of respiratory system
– Mesoderm- middle layer
• Gives rise to muscles and much of the circulatory,
excretory, and reproductive systems
– Ectoderm- outermost layer
• Gives rise to sense organs, nerves, and outer layer of
the skin
Body Symmetry
• All animals, except sponges, exhibit some kind
of body symmetry
• Radial symmetry- body parts repeat around
the center of the body
• Ex: starfish, anemones
• Bilateral symmetry- a single imaginary plane
divides the body into 2 equal halves
– Typically have left and right sides, upper and lower
sides and front and back ends
Radial vs. Bilateral Symmetry
Bilateral Symmetry
Bilateral Symmetry
Bilateral symmetry
Anterior
Posterior
Bilateral Symmetry
• Allows for segmentation- a body constructed of
many repeated and similar parts, or segments
– Combination of bilateral symmetry and segmentation
found in two of the most successful groups of
animals: arthropods and vertebrates
Cephalization
• Refers to the
concentration of sense
organs and nerve cells at
the front end of the body
– Called the head
• Response to environment
is quicker and more
complex than in simpler
animals
Body Cavity Formation
• Refers to the space between the digestive tract
and the body wall
• Provides safe space for internal organs
• In some organisms contain fluids for circulation,
feeding, and excretion
• Coelom- is a true body cavity that develops
within the mesoderm and is lined with tissue
derived from mesoderm
– Acoelomate- refers to an organism that lacks a
coelom
• Psuedocoelom- partially lined with mesoderm
Coelomate vs. Pseudocoelomate
Sponges
•
•
•
•
Phylum Porifera
Sessile as adults
Contain a few specialized cells
Basically a cylindrical (yet asymmetrical) water
pump
• Use choanocytes, specialized cells with
flagella, to help move water through the
sponge
Water Movement in Sponges
• Water moves via pores into the central cavity
and out the opening at the top called an
osculum
Water Movement in Sponges
As water moves through the sponge:
• Food particles are filtered from the water
• Wastes are removed from the sponge
• Simple mechanism for:
– feeding
– respiration
– circulation
– excretion
More on Sponges
• Have simple skeletons
– Harder sponges have skeletons made of spicules of
CaCO3 or silica
• Made by archaeocytes
– Softer sponges made of spongin- flexible protein
fibers
• Filter feeders
– Choanocytes pass food on to archaeocytes for further
digestion
• Sponges lack a nervous system, but produce
toxins to deter predators
Reproduction
• Can reproduce sexually or asexually
• Sexual reproduction:
– Most sponge species make both eggs and sperm,
but gametes are produced at different times
– Eggs are fertilized by internal fertilization
• Archaeocytes carry sperm to eggs located in the walls
of the sponge
– Fertilized eggs develop into motile larvae that are
carried away by ocean currents
Reproduction
Asexual reproduction:
• Two methods are budding and gemmules
– Budding- piece of a sponge breaks off and grows
into a new sponge
– Gemmules- groups of archaeocytes surrounded
by a layer of spicules
• Can survive freezing temperatures and drought
Cnidarians
•
•
•
•
Soft-bodied
Carnivorous
Radial symmetry
Tentacles arranged in circles around their
mouths
– Tentacles contain cnidocytes or stinging cells that
are armed with nematocysts-poison filled stinging
structures
Cnidarian Diversity
Name that jelly!
Cnidarian Life Cycle
• Typical life cycle includes both a polyp and a
medusa stage
• Polyp- sessile, cylindrical, with mouth upward
• Medusa- motile, bell-shaped, with mouth on
the bottom
Reproduction
Body Systems
• Digestion takes place extracellularly in the
gastrovascular cavity
– Partially digested food is absorbed into cells where it
is then completely digested
• Respiration, circulation, and excretion via
diffusion
• Response via a nerve net that detects stimuli
– Statocysts aid in gravity detection
– Ocelli- eyespots that detect light
• Movement by means of hydrostatic skeleton or
jet propulsion
Flatworms
• Phylum Platyhelminthes
• Simplest of animals
displaying bilateral
symmetry
• Live in marine,
freshwater, or damp
terrestrial habitats
• Some parasitic, others
free-living
Flatworm Groups
Three major groups:
1. Planarians (free-living)
– Heads with lightsensitive eye spots
– Flaps to detect chemicals
– Dense clusters of nerve
cells that form a simple
brain and a pair of nerve
cords that run the length
of the body
– Branched gastrovascular
cavity with a single
opening
Flatworms
2. Flukes– Parasitic
– Complex life cycles
– Suckers to attach to host
3. Tapeworms
– Parasitic
– Ribbon-like body with repeating
units
– Anterior scolex armed with hooks
and suckers to attach to host
– Absorb nutrients directly across
body surface
– Units at posterior end hold eggs
that pass out of host’s body
Nematodes
• Phylum Nematoda
– Called nematodes or roundworms
• Abundant and diverse (~500,000 species)
– Humans host at least 50 species
• Bilateral symmetry
• 3 germ layers
• Nonliving cuticle layer to prevent them from
drying out
• Pseudocoelom functions to distribute nutrients
and as a hydroskeleton
• Complete digestive tract with mouth and anus
Annelida
• Phylum Annelida
– Called segmented worms
• True coelom that functions as a hydrostatic skeleton
• Nervous system with simple brain and ventral nerve
cord
• Closed circulatory system- blood remains in vessels
throughout the body
• Found in damp soil, the sea and most freshwater
habitats
• Includes earthworms, polychaetes, and leeches
leech
earthworm
Polychaete
Mollusks
• Phylum Mollusca
Characteristics:
• Soft-bodied with internal or external shell
– Ex: snails, squids, clams and octopi
• Free swimming larval stage called a
trochophore
Groups of Molluscs
• Gastropods- shell-less or single shelled, move by
a muscular foot on ventral side
– pond snails, land slugs, sea butterflies, sea hares,
limpets, and nudibranchs
• Bivalves- 2 shells held together by powerful
muscles
– Clams, oysters, scallops
• Cephalopods- head is attached to single foot that
is divided into tentacles or arms
• Nautiluses, squids, octopi, and cuttlefish
Body Plan
• Mollusks are variations of a single body plan
including:
– Foot- forms vary from flat for crawling to tentacles
for swimming
– Mantle- thin layer of tissue that surrounds entire
body
– Shell- made from CaCO3 secreted by glands in
mantle
– Visceral mass- contains internal organs
Mollusk functions
Feeding- all trophic levels
• Some use radula- a flexible tongue shaped
structure with many teeth used to scrape and
grind food
– snails and slugs
• Jaws
– octopi and some sea slugs
• Filter feeding using water carried through a
siphon
– scallops, oysters, and clams
Mollusk functions
Respiration
• Gills (aquatic) or mantle cavity lined with blood
vessels (terrestrial)
Circulation
• via open circulatory system
– blood is pumped through vessels to open sinuses,
large sac-like spaces, to gills, and back to heart
Excretion
• nephridia remove nitrogen containing waste out
of the body
Mollusk functions
Response varies greatly
• Octopi have the most highly developed
nervous systems of all inverts
Movement
• Mucus gliding, jet propulsion
Reproduction
• Externally in snails and two-shelled mollusks
• Internally in tentacled mollusks and some
snails
Arthropods
• Phylum Arthropoda
Characteristics
• Segmented body
• Tough exoskeleton made of chitin
• Jointed appendages- structures that extend
from the body wall
Groups of Arthropods
• Classification is based on the number and
structure of their body segments and
appendages- especially mouthparts
• Three major groups:
– Crustaceans
– Spiders
– Insects
Arthropod Groups
• Crustaceans
• 2 antennae, 2 or 3 body segments, chewing
mouthparts called mandibles
• Mostly aquatic, but includes terrestrial
pillbugs
– Ex: lobsters, crayfish, barnacles
Spiders
• Spiders and their relatives (subphylum
Chelicerata) includes:
– Horseshoe crabs, spiders, ticks, and scorpions
• Mouthparts called chelicerae, 2 body sections,
and most have 4 pairs of walking legs
– Lack antennae
• Paired pedipalps are usually modified to grab
food
– Claws in scorpions
Insects
• Insects and their relatives (subphylum
Uniramians) include:
• Insects as well as centipedes and millipedes
Insect Relatives
Centipedes
Millipedes
• Few to 100 pairs of legs
• Each segment contains a
pair of legs
• Carnivorous
• Venom producing
• Water loss limits their
habitat to moist or humid
areas
• Each segment contains 2
pairs of legs
• Feed on dead and decaying
plant material
• May secrete unpleasant or
toxic chemicals
Insects
• Account for 73% of all animal diversity
• Insect bodies are divided into 3 parts: head,
thorax, and abdomen
• 3 pairs of legs attached to the thorax
• Typically, also have:
–
–
–
–
A pair of antennae
Compound eyes
Two pairs of wings
Tracheal tubes for respiration
Insect Societies
Arthropod Functions
Feeding- variety of mouthparts, form follows function
• Ex: butterfly mouth (proboscis) functions as a straw
Respiration
• Terrestrial
– Most breath through tracheal tubes that open to the outer
environment via openings called spiracles
– Some use book lungs (spiders)
• Aquatic
– feather like gills or book gills (horseshoe crab)
Arthropod Functions
Circulation
• Open circulatory system
Excretion
• Terrestrial- wastes eliminated via Malpighian
tubules- sac-like organs that extract wastes
from blood
• Aquatic- diffusion from cells into surrounding
water
Arthropod functions
Response
• All have brain and two nerves that encircle the esophagus
and connect brain to ventral nerve cord
• Ganglia, groups of nerve cells, along nerve cord coordinate
movement
Movement
• Muscles are coordinated by nervous system
• Generate force by contracting and pulling on exoskeleton
Reproduction
• Terrestrial- internal fertilization
• Aquatic- internal or external
Growth and Development
• Arthropods undergo a process called moltingshedding their exoskeleton and growing a
new, larger one
Complete vs. Incomplete
Metamorphosis
Echinoderms
• Phylum Echinoderms
Characteristics include:
• Endoskeleton- formed of hardened plates of
CaCO3
• Spiny skin
• Water vascular system
• Tube feet
• As adults, radial symmetry (no anterior or
posterior end) and no cephalization
– Larvae display bilateral symmetry
Echinoderm functions
• Water vascular system
• Water enters through madreporite which
connects to ring canal that extends out to
each leg
• Tube feet are connected to ring canal
– Alternating contractions, caused by water
movement into tube feet, and relaxations of
muscles move echinoderms
functions
Feeding varies
Respiration and Circulation
• diffusion across thin membrane on tube feet or gills in
some species
Excretion
• diffusion across thin membrane on tube feet or solid
wastes out anus
Response
• via nerve ring and scattered sensory cells
Reproduction
• external fertilization, 2 separate sexes in most species
• offspring, called larvae, have bilateral symmetry
Groups of Echinoderms
1. Sea stars
2. Brittle stars
3. 3. Sea cucumbers
4. Feather stars
5. Sea Urchins and sand dollars
Sea lilies (inset)