Chapter 31

Chapter 31 - Animal Origins and the Evolution of Body Plans...

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Animal Origins and the Evolution of Body Plans 31.1 What Characterisitcs Distinguish the Animals? Animal Traits o Multicellular o Develop from a single cell o Heterotrophs o Internal digestion o Most can move Resolve evolutionary relationships using: o Fossils o Protein structure o Gene sequences o Development Cleavage of the fertilized zygote: Incomplete cleavage- the dividing cells form an embryo on top of the yok mass (reptiles) Radial cleavage- even division of yolk (sea urchins, echinoderms) Spiral cleavage- uneven division of yolk (insects) Cell Layers Diplobalstic- animals have 2 cell layers—ectoderm and endoderm Triploblastic- have 3 layers—ecto, endo, and mesoderm Gastrulation (Triploblasts) Protosomes (mouth first): the blastopore develops into the mouth. Deuterostomes ( mouth second): the blastopore develops into the anus; the mouth develops later Together these groups are the bilaterians (have bilateral symmetry) 31.2 What are the Features of Animal Body Plans?
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Chapter 31 - Animal Origins and the Evolution of Body Plans...

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