Echinoderms Deuterostomes

Echinoderms or Deuterostomes are marine and are starfish, sea urchins and sea slugs. Compared to insects, echinoderms are large, cold, slow-moving bottom dwellers. Echinoderms have endoskele-tons beneath their skins or epidermis. Endoskeletons are spines or plates having a radial symmetry (starfish), and in some instances, symmetry is bilateral (sea cucumber). Fine networks of branching crystals of calcium carbonate, stereoms, are the building blocks of the interlocking plates or spines. Deuterostomes have an extensive body cavity that for embryonic reasons, is not a hemocoel but a coelom. Like a hemocoel, the coelomic cavity contains fluid and is lined with tissue, so that nutrients and wastes must traverse this interface. In deuterostomes, a water vascular system, a set of water-filled canals, radiates from a ring canal around the gut. The radial canals lead to podia or tube feet on the surface of the body. Tube 'feet' extend and retract according to changes in hydrostatic pressure within the water vascular system. Because deuterostomes are cold and slow-moving, open circulations can supply the low metabolic needs of these animals.

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