ECHINODERMS

Exclusively a marine phylum, echinoderms are found intertidally to great depths. As adults almost all forms are benthic (living on the ocean's floor). Most are characterized by a calcareous (calcium carbonate) skeleton , external spines or knobs and a pentamerous ( five sided) radial body symmetry. Chambers and tubes in the body make up an elaborate hydraulic system (water vascular) that operates hundreds of tubed feet, which are used in feeding, locomotion, and respiration. There are 5 classes of Echinoderms. Echinoidea are spiny herbivores and include sea urchins and sand dollars. Asteroidea are seastars, formally star fish, which are further discussed on the Sea Stars page. Holothuroidea are sea cucumbers, which are sausage shaped and have a mouth at the end of their body - instead of in the middle. Their body wall is muscular with reduced skeletal plates and spines. They are detritivores (filter feeders), feeding mostly on digested sediment by the use of mucus covered tentacles around the mouth. A few feed on plankton. Class Ophiuroidea are brittle stars, which are different than true seastars. Mostly nocturnal, or found in greater depths, they are characterized by long, snaky, flexible arms with small tube feet extending from them. They move not by pacing with their tubed feet, like true sea stars, but by "rowing" with their long arms. Ingested phytoplankton's metabolically altered carotenoid pigments give brittle stars their color. The last class is Crinoidea, which include Sea Lilies.

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