Chapter 33

Chapter 33 - Chapter 33 What is a Deuterostome 33.1 What us...

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Chapter 33: What is a Deuterostome? 33.1 – What us a Deuterostome? o Deuterostomes are a diverse group of animals that display 3 features Radial cleavage During embryonic development, the blastopore develops into the anus (instead of the mouth) Coelom develops from mesodermal pockets during gastrulation instead of splitting of the mesoderm o Radial cleavage is not exclusive to deuterostomes o Complex behaviors are well adapted in deuterostomes o Deuterostomes have 3 distinc clades Echinoderms – which include sea stars, sea urchins, and relatices Hemichordates – including acorn worms and pterobranchs Chordates – including sea squirts, lancelets, and vertebrates o Deuterostomes evolved from an organism with pharyngeal slits and bilateral symmetry o Therefore, echinoderms probably reverted to radial symmetry secondarily o Although they are radially symmetrical as adults, they are bilateral as larvae (showing proof of ancestry) 33.2 – What are the major groups of echinoderms and hemichordates? o Echinoderms and hemichordates are collectively known as ambulacrarians o Echinoderms exhibit pentaradial symmetry calcified internal skeleton water vascular system tube feet oral (mouth containing) side and aboral (back) side
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o water vascular system used for gas exchange locomotion feeding o most surviving echinoderms are both sessile and motile grouped into echinozoans (sea urchin and cucumber) and asterozoans (sea stars and brittle stars) o sea stars can generate enough power to grab bivalves and open them to eat them o hemichordates are wormlike marine deuterostomes which have a proboscis – feeding tube a collar – which bears the mouth a pharynx – muscles near proboscis a trunk – contains other body parts and pharyngeal slits – to let water out 33.3 – What new features evolved in the chordates?
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Chapter 33 - Chapter 33 What is a Deuterostome 33.1 What us...

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