Echinoderms

Echinoderms, of the phylum Echinodermata, include sea stars (starfish), sea urchins, sand dollars, sea cucumbers, and brittle stars. Characteristics of echinoderms:

• live only in the sea or a marine environment
• very diverse in shape, but most have a hard, spiny skin
• body parts are organized around a central point ("radial symmetry"), often with five body parts
• internal vessels circulate water instead of blood