BIO 200 Lecture Notes - Lecture 20: Hemichordate, Crinoid, Madreporite
27 Jun 2015
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Document Summary
Deuterostomes: mouth develops after anus, monophyletic group, have internal skeletons and internal segments, ambulacrarians: echinoderms and hemichordates, ancestral deuterostomes (homalozoans) had traits found in modern ambulacrarians. Symmetry: chordates: lancelets, tunicates, and vertebrates. Old body grows new limb: may drop body parts when attacked, may be possible to break in half and completely regenerate. 20 extinct classes: three extant groups: crinoids, echinozoans, and asterozoans. Echinozoans: have no arms, more difficult to see symmetry, example: sea urchins, hemispherical (has a flat bottom, many spines. Sting anything they touch: example: sand dollars, example: sea cucumbers, may look bilateral, but is actually radial (cut across, anterior mouth and posterior anus, tube feet (attachment) Hemichordates: acorn worms, three parts: collar, proboscis, and stalk. Swimming tadpole larvae shows relationship to vertebrates: lancelets. Gonads swell up and burst into water during reproduction: animal dies in order to reproduce.
