Chapter 28
An Introduction to Animal Diversity
Characteristics of Most Animals
• 1. multicellular eukaryotes
• 2. cell specialization
– (cells  tissues  organs)
•
•
•
•
3. heterotrophs
4. locomotion (sometime in lifecycle)
5. nervous + muscle systems (stimuli)
6. sexual reproduction
– (large, nonmotile eggs; flagellated sperm)
Marine Environments
• Advantages
– Buoyancy – support
– Temperature – stable
– Fluid + salt balance easily maintained
• Challenges
– Water movement/currents
• Adapt:
–
–
–
–
Strong swimmer – squid, fish, mammals
Sessile
Burrow in sand/silt
Small body size  plankton (food supply around as tossed)
Other environments - problems
• Fresh water
– Water hypotonic to animal fluids 
• Osmoregulation - pump out water, keep salts
(ATP)
– Less constant
– Less food
– Oxygen and temp. vary
– Turbidity + water volume change
• Land
– Desiccation
• Adapt: body covering; respiratory surface deep
within animal
– Reproduction (desiccation)
• Adapt: internal fertilization; shells on eggs; embryo
in mom
– Temperature extremes
Body Symmetry
• 2 types
– Radial
• wheel or cylinder form
• Spokes from central axis
– Cnidarians – jellyfish, sea anemones
– Echinoderms – sea stars
– Bilateral
• Right and left halves – mirror images
Fig. 32-7
(a) Radial symmetry
(b) Bilateral symmetry
Types of Body Cavities
• Coelom = fluid-filled space between body
wall and digestive tube
• Acoelomate
– No body cavity
• Pseudocoelomate
– Body cavity, not lined with mesoderm
• Coelomate
– Body cavity completely lined
Fig. 32-2-3
Blastocoel
Cleavage
Endoderm
Cleavage Blastula
Ectoderm
Zygote
Eight-cell stage
Gastrulation
Blastocoel
Cross section
of blastula
Gastrula
Blastopore
Archenteron
Fig. 32-8
Coelom
Digestive tract
(from endoderm)
Body covering
(from ectoderm)
Tissue layer
lining coelom
and suspending
internal organs
(from mesoderm)
(a) Coelomate
Body covering
(from ectoderm)
Pseudocoelom
Muscle layer
(from
mesoderm)
Digestive tract
(from endoderm)
(b) Pseudocoelomate
Body covering
(from ectoderm)
Tissuefilled region
(from
mesoderm)
Wall of digestive cavity
(from endoderm)
(c) Acoelomate
2 Main Groups of Coelomates
• Protostomes
– “first, the mouth”
– Mollusks, annelids, arthropods
• Deuterostomes
– “second, the mouth”
• Echinoderms, chordates
Protostomes vs. Deuterostomes
Cleavage
• Protostomes
– Spiral
• Deuterostomes
– radial
Fig. 32-9a
Protostome development
(examples: molluscs,
annelids)
Eight-cell stage
Spiral and determinate
Deuterostome development
(examples: echinoderms,
chordates)
Eight-cell stage
Radial and indeterminate
(a) Cleavage
Protostomes vs. Deuterostomes
Developmental Fate of the Embryo
• Protostomes
– “determinate”
cleavage
– Fixed early
– Can only become
certain cell types
• Deuterostomes
– “indeterminate”
cleavage
– Can adapt to become
another cell type
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.
Protostomes vs. Deuterostomes
Blastopore = (opening from outside to gut)
• Protostomes
– Develops into the
mouth
• Deuterostomes
– Develops into the anus
– Later, 2nd opening
makes mouth
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
Sponges – Phylum Porifera
• “to have pores”
• Bodies – tiny holes
• Marine
Fig. 33-3a
A sponge
3 main classes of sponges
• Calcarea
– Chalky, calcium carbonate spikes (spicules)
• Hexactinellida (glass sponges)
– 6-rayed spicules with silica
• Demospongiae
– Variable
• Fibrous protein = spongin
• Silica
• OR spongin + silica
Fig. 33-4
Choanocyte
Osculum
Flagellum
Collar
Food particles
in mucus
Choanocyte
Azure vase sponge (Callyspongia
plicifera)
Spongocoel
Phagocytosis of
food particles
Pore
Epidermis
Spicules
Water
flow
Amoebocytes
Mesohyl
Amoebocyte
Sponge Anatomy
• Spongocoel
– Central cavity – water
flows
• Ostia
– Tiny pores, water
enters
• Osculum
– Open end, water exits
• Epidermal cells
– Outer layer, line
canals
Sponge Anatomy
• Canals
– SA – food capture
• Porocytes
– Tube like cells – form
pores
– Regulate diameter by
contracting
• Collar cells
Sponge Anatomy
• Collar cells
– Inner layer
– Create water current,
bring food and water
to cells, carries away
waste and CO2
– Trap and phagocytize
food
– Tiny collar at base of
flagellum
Sponge Anatomy
• Mesohyl
– Gelatin-like layer
– Between inner and
outer layers of sponge
body
• Amoebocytes
– In mesohyl
– Digestion, food
transport, secrete
spicules
Sponge Feeding
• Suspension feeders
– Trap + eat whatever food the water brings
– Water circulates in body
– Food trapped on sticky collars of choanocytes
– Food digested in collar or amoeboid cell
– Undigested – out to water through osculum
Gas exchange/Excretion
• Diffusion – in/out of individual cells
Response to Stimuli
• No special nerve cells – can’t react as a
whole
• Individual cells can respond
Reproduction of sponges
• Asexual
– Fragment or bud
• Sexual
–
–
–
–
Hermaphrodite – egg + sperm
Some amoeboid cells become sperm, some eggs
Eggs/sperm made at different times  cross fertilize
Sperm released into water, taken in by other sponges
of same species
– Fertilization and early dev. In mesohyl
– Embryo moves to spongocoel, leaves with water
– Swims, attaches to solid object  sessile
Cnidarians – Phylum Cnidaria
• marine
• Solitary
• colonies
Fig. 33-3b
A jelly
3 classes of Cnidarians:
• Hydrozoa
– Hydras, hydroids
– Polyp dominant
• Scyphozoa
– Jellyfish
– Medusa dominant
• Anthozoa
– Sea anemones, corals
– No medusa
Fig. 33-7
(b) Jellies (class
Scyphozoa)
(a) Colonial polyps (class
Hydrozoa)
(c) Sea wasp (class
Cubozoa)
(d) Sea anemone (class
Anthozoa)
Body of Cnidarians
• Radial symmetry
• Hollow sac w/ mouth + surrounding
tentacles at 1 end
• Mouth leads to GV cavity (digestive)
• Mouth – ingests food, expels waste
• Epidermis
– Protective covering
• Gastrodermis
– Lines gut, digestive
• Mesoglea
– Gelatinous, acellular
– Separates epidermis + gastrodermis
2 body shapes of Cnidarians
• Polyp
– Dorsal mouth w/ tentacles
– Hydra
• Medusa
– Mouth on lower oral surface
– Jellyfish
Fig. 33-5
Mouth/anus
Polyp
Tentacle
Medusa
Gastrovascular
cavity
Gastrodermis
Body
stalk
Mesoglea
Epidermis
Tentacle
Mouth/anus
Response in Cnidarians
• Nerve nets
– Nerve cells that connect sensory cells in body
wall to contractile + gland cells
– Cells contacted, entire body responds –
crunches in
Feeding in Cnidarians (hydra)
• Paralyze prey with Nematocysts
– Nematocysts
•
•
•
•
Stinging cells (“thread capsules”)
In cnidocytes
Stimulated – release coiled, hollow thread
Sticky OR long and coil around prey OR
barbs/spines
• Prey pushed into mouth
• GV cavity – digestion
– Body motion helps circulate contents
Fig. 33-6
Tentacle
Cuticle
of prey
Thread
Nematocyst
“Trigger”
Thread
discharges
Cnidocyte
Thread
(coiled)
Gas exchange/Excretion
• Diffusion
– No cell far from surface
Reproduction in Cnidarians
• Asexual
– Budding – good conditions
– Colony – buds remain on parent
• Sexual
– Fall or stagnant water
– Become males and females
• Female – ovary – single egg
• Male – testis - sperm
– Zygote – may become covered with shell for winter
Fig. 33-8-3
Feeding
polyp
Reproductive
polyp
Medusa
bud
ASEXUAL
REPRODUCTION
(BUDDING)
Portion of
a colony
of polyps
Haploid (n)
Diploid (2n)
Gonad
Medusa
Egg
SEXUAL
REPRODUCTION
Sperm
FERTILIZATION
Zygote
1 mm
Key
MEIOSIS
Developing
polyp
Mature
polyp
Planula
(larva)
Comb Jellies – Phylum Ctenophora
•
•
•
•
Marine
Luminescent
8 rows cilia (comb)
2 tentacles – no nematocysts – adhesive glue
cells
• Radial symmetry
• 2 cells layers w/ mesoglea
• Mouth – food in; 2 anal pores – waste out (other
end)
Fig. 33-3d
A ctenophore, or comb jelly
Flatworms – Phylum
Platyhelminthes
• Flat, elongated, acoelomate
• Bilateral symmetry
• Cephalization
– “head” at anterior – moves forward; eyespots
• 3 germ layers –
– ectoderm, mesoderm, endoderm
• Muscular pharynx
– Takes in food – 1 opening mouth
Flatworms cont.
• Nervous system
– Simple brain = 2 mass nerve tissue = ganglia
– connect to 2 nerve cords
• Protonephridia
– Osmoregulation, waste disposal
• Complex reproductive organs
• No organs for circulation, gas exchange
– Diffusion through body wall
Fig. 33-3e
1.5 mm
Acoel flatworms (LM)
Fig. 33-3f
A marine flatworm
3 classes of Flatworms
• 1. Turbellaria
– Free-living
– Planarians – pond
•
•
•
•
Crossed eyes
Auricles (“ears”) – locate food
Carnivore – mouth, pharynx, GV cavity
Reproduction
– asexual – splits in 2
– Sexual – hermaphrodite – cross-fertilization
Fig. 33-10
Pharynx
Gastrovascular
cavity
Mouth
Eyespots
Ganglia
Ventral nerve cords
• 2. Trematoda + Monogenea
– Flukes – blood + liver
– Parasites
– Hooks, suckers – attach to host
– Complex reproduction
Fig. 33-11
Male
Female
Human host
1 mm
Motile larva
Ciliated larva
Snail host
• 3. Cestoda
– Intestinal parasite
– Tapeworm – long, flat, ribbon-like
– Suckers, hooks on scolex (head)
– Body – proglottids (segments)
• Each proglottid – male and female organs
(100,000 eggs)
– No mouth/digestive sys. – diffusion
– Lacks sense organs
Fig. 33-12
200 µm
Proglottids with
reproductive structures
Hooks
Sucker
Scolex