Biology 3229F/G Study Guide - Final Guide: Synapomorphy, Aplacophora, Cephalochordate
21 Apr 2016
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Phylogeny recapitulates ontogeny the idea is that the embryo goes through the phylogenic tree as it develops to reach final stage. Larger foot allows it to dig deeper and require less protection from the outside. 20 species looks like half a bivalve. Kind of sort of displays segmentation, but they don"t have molluscs with segmentations ctenidium = gills. Once torsion occurs, bilateral symmetry goes away. Torsion exists because they can fit into shell easier. Key features of molluscs shell, radula, foot. Counter current exchange (can take more oxygen out of the water) Large complex brain (8 arm brains control the arms) + main brain. Arms have suckers for squid (sometimes with a tooth in each sucker) 5 classes: asteroidean (sea star), crinoidea (most basal), echinoidea (urchins), ophiuroidea (brittle stars), holothuoidea (sea cucumber) Larvae is bilateral symmetry; adult has pentaradial symmetry ossicles. Tube foot applies the stuff to stick to substrate.
