Each animal phylum has a unique body plan. • Vertebrates

have an internal segmented backbone.

• Invertebrates do not have a backbone.

• Invertebrates encompass most animal groups.

Three criteria are used to categorize animals1. Body plan symmetry– Bilateral: body divides

equally along one plane (mirror images)

– Radial: body arranged in a circle around a central axis

2. Tissue layers– Bilateral have 3 distinct

layers– Radial have 2 distinct

layers3. Developmental patterns– Protostomes: mouth first,

anus second– Deuterostomes: anus first,

mouth second

Protostomes Deuterostomes

Protostomes and deuterostomes are the two major radiations on the animal phylogenetic tree. – Based on anatomical and molecular evidence

Porifera Cnidaria Platyhelminthes AnnelidaMollusca Nematoda Arthropoda

EchinodermataChordata

RADIALRADIAL

NO TISSUESNO TISSUES

PROTOSTOMES

DEUTEROSTOMES

jelly

fish,

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nem

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spon

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flatw

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Segm

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clam

s, sn

ails

,oc

topu

ses

roun

dwor

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crus

tace

ans,

inse

cts,

spid

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sea

star

s,

sea

urch

ins

lanc

elet

s,ve

rteb

rate

s

Porifera• AKA: Sponges• Most primitive

animals– 570 myo, >9000

species– Specialized cells,

but no true tissue– Closely related to

protists– Neither

protistomes or deuterostomes

Shared characteristics– Sessile– Filter feeders– Specialized cells include:• Spicule: skeletal like cells;

spongin, silica, or CaCO3

• Pinacocytes: outer layer• Choanocytes: inner layer,

each has a flagellum• Amoebocytes: middle layer,

absorb and digest

Sponge Reproduction– Reproduce sexually or

asexually• Sexual

– Hermaphrodites, producing eggs/sperm at different times

– Sperm is released, captured by female of same species

– Ciliated larvae form from zygote

• Asexual– Budding: small piece breaks off, but

can still survive

Cnidaria• AKA: Stinging nettles– Nematocyst: capsule

with a poison barb at one end

• > 9000 aquatic species• Mobile• Two body forms– Polyp– Medusa

• Gastrovascular cavity

Cnidarian Reproduction• Sexually: mostly medusa-– Gametes released in water– Zygote develops into free-swimming larva,

called planula

• Asexually: mostly polyps-budding

The four major cnidarian classes are defined by their dominant body form.

– Anthozoans such as sea anemones have a dominant polyp stage.

– Hydrozoans such as hydra alternate between forms.

– Scyphozoans are jellyfish with a dominant medusa form.

– Cubozoans such as sea wasps have a dominant medusa form.