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© Cengage Learning 2015
Chapter 23:
Invertebrate
Animals
© Cengage Learning 2015
What is an animal?
Eukaryotic, multicelled heterotrophs
without cell walls
© Cengage Learning 2015
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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© Cengage Learning 2015
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)
© Cengage Learning 2015