The phylum Echinodermata contains over 6000 species. This phylum includes the sea stars, brittle stars, sea urchins and sea cucumbers.Its name comes from the Greek meaning "spiny skin" since their endoskeleton is made of hard calcium carbonate plates.There are five classes of echinoderms: Asteroidea (sea stars), Ophiuroidea (brittle stars), Echinoidea (sea urchins), Crinoidea (feather stars) and Holothuroidea (sea cucumbers). In general, all echinoderms have a five-part radial symmetry, a water vascular system, structures called tube feet and they live only in salt water.
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