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Chapter 23:

Invertebrate

Animals

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What is an animal?

Eukaryotic, multicelled heterotrophs

without cell walls

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Evolution of the animal body plan

Tissue organization: Ectoderm – outer layer

Mesoderm – middle layer

Endoderm – inner layer

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Animal body plans: Symmetry

Radial

symmetry

Bilateral

symmetry

Top

Bottom

Dorsal

Ventral Anterior end

Posterior end

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Body plans: Types of body cavity

1. Coelomate: Body cavity completely lined

by tissue derived from mesoderm

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Body plans: Types of body cavity

2. Pseudocoelomate: Body cavity partially

lined by tissue derived from mesoderm

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Body plans: Types of body cavity

3. Acoelomate: Lack coelom altogether

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Protostomes vs Deuterostomes

• Protostome: First opening on embryo becomes mouth

• Deuterostome: Second opening on embryo becomes mouth

Protostome Deuterostome

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Colonial Theory of Animal Origins

• Scientists hypothesize that animals evolved from

a colonial flagellated protist.

• The oldest animal fossils found are 550–575

million years old.

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Sponges (Phylum Porifera)

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Jellyfish, Corals (Phylum Cnidaria)

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Flatworms (Phylum Platyhelminthes)

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Segmented Worms (Phylum Annelida)

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Claims, Snails, Octopi (Phylum Mollusca)

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Roundworms (Phylum Nematoda)

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Insects, Crustaceans (Phylum Arthropoda)

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Insect Ecology

Dung beetles. Nature’s clean-up crew. Dung

beetles feed on feces. The beetles sniff out their

stinky food, then form it into balls that they roll

away and bury.

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Starfish, sand dollars, sea urchins

(Phylum Echinodermata)

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