94 C. Dissection of the Sea star: The members of the phylum Echinodermata are entirely marine; they have bilateral larvae but show secondary radiality as adults, have a spiny calcareous endoskeleton, and possess a well-developed coelom that includes a unique manifestation, the water vascular system . The water vascular system functions as a network of hydraulic canals that are involved with locomotion, feeding, and gas exchange in echinoderms. Echinoderms are triploblastic organisms with a complete digestive tract (though the anus is vestigial in some). Although the number of arms is quite variable, pentamerous symmetry is the most common arrangement; a typical sea star will have 5 arms or rays, which arise from a central disk . Rays normally are the same size; if smaller ones are present, they are being regenerated following injury to the sea star. As you follow dissection instructions below, label the diagram provided. External Features:
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