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3. water vascular system instead of muscles is a big advantage in predatory situations
4. highly regenerative - can regrow lost or damaged body parts
5. separate sexes; external fertilization
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Why are they considered simple?
1. Light-sensitive eyes located at the end of each ray do not provide vision because there is no brain nor head.
2. They have reduced internal organs - no respiratory, circulatory, excretory. No nervous system.
4. Adults have pentamerous (5-fold) radial symmetry (associated with sedentary lifestyle)5. Respiration is by diffusion through the skin.
3. Nerve net (no nervous system) – exhibit complex behavior
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Seastars are predators and eat a variety of organisms.http://www.youtube.com/watch?v=ALaMoS_vvNE
The seastar can open a clam shell a few millimeters wide.
Then by everting its stomach into the shell, the clam is digested and absorbed. http://www.youtube.com/watch?v=A100m5EpfFI Seastar Eating a Clam Missing parts from injuries or evisceration are quickly replaced. Any portion of the central disk will regenerate a new seastar - a fact that oyster fishermen learned too late!