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

Zygote

Cleavage

Eight-cell stage

Cleavage Blastula

Cross sectionof blastula

Blastocoel

Gastrulation

BlastoporeGastrula

Archenteron

Ectoderm

Endoderm

Blastocoel

Fig. 32-8Coelom

Body covering(from ectoderm)

Digestive tract(from endoderm)

Tissue layerlining coelomand suspendinginternal organs(from mesoderm)

(a) Coelomate

Body covering(from ectoderm)

Pseudocoelom

Digestive tract(from endoderm)

Muscle layer(frommesoderm)

(b) Pseudocoelomate

Body covering(from ectoderm) Tissue-

filled region(frommesoderm)

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. DeuterostomesCleavage

• Protostomes– Spiral

• Deuterostomes– radial

Fig. 32-9a

Eight-cell stage Eight-cell stage(a) Cleavage

Spiral and determinate Radial and indeterminate

Protostome development(examples: molluscs,

annelids)

Deuterostome development(examples: echinoderms,

chordates)

Protostomes vs. DeuterostomesDevelopmental 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

Coelom

Protostome development(examples: molluscs,

annelids)

Deuterostome development(examples: echinoderms,

chordates)

(b) Coelom formation

Key

EctodermMesoderm

Endoderm

MesodermMesoderm

Coelom

Archenteron

Blastopore Blastopore

Solid masses of mesodermsplit and form coelom.

Folds of archenteronform coelom.

Protostomes vs. DeuterostomesBlastopore = (opening from outside to gut)

• Protostomes– Develops into the

mouth

• Deuterostomes– Develops into the anus– Later, 2nd opening

makes mouth

Fig. 32-9c

Anus

Protostome development(examples: molluscs,

annelids)

Deuterostome development(examples: echinoderms,

chordates)

Anus

Mouth

Mouth

Digestive tube

(c) Fate of the blastopore

Key

EctodermMesoderm

Endoderm

Mouth develops from blastopore. Anus develops from blastopore.

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

Azure vase sponge (Callyspongiaplicifera)

Spongocoel

Osculum

Pore

Epidermis Waterflow

Mesohyl

Choanocyte

Flagellum

Collar

Food particlesin mucus

Choanocyte

AmoebocytePhagocytosis offood particles

Spicules

Amoebocytes

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

(a) Colonial polyps (class Hydrozoa)

(b) Jellies (class Scyphozoa)

Sea wasp (classCubozoa)

(d) Sea anemone (class Anthozoa)

(c)

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

PolypMouth/anus

Bodystalk

Tentacle

Gastrovascularcavity

Gastrodermis

Mesoglea

Epidermis

TentacleMouth/anus

Medusa

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

Nematocyst

“Trigger”

Cuticleof prey

Threaddischarges

Thread(coiled)

Cnidocyte

Thread

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

Feedingpolyp

Reproductivepolyp

Medusabud

Medusa

ASEXUALREPRODUCTION(BUDDING)Portion of

a colonyof polyps

1 m

m

Key

Haploid (n)Diploid (2n)

Gonad

SEXUALREPRODUCTION

MEIOSIS

FERTILIZATION

Egg Sperm

Zygote

Planula(larva)

Developingpolyp

Maturepolyp

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

Acoel flatworms (LM)

1.5 mm

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

Gastrovascularcavity

Mouth

Eyespots

Ganglia Ventral nerve cords

• 2. Trematoda + Monogenea– Flukes – blood + liver– Parasites– Hooks, suckers – attach to host– Complex reproduction

Fig. 33-11

Human host

Motile larva

Snail host

Ciliated larva

Male

Female

1 mm

• 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

Proglottids withreproductive structures

Hooks

Sucker

Scolex

200 µm