Echinoderms are characterized by the following traits: radial symmetry, several arms radiating from a central body. The body consists of five equal segments, each containing a duplicate set of various internal organs. They have no heart, brain, nor eyes, but some brittle stars seem to have light sensitive parts on their arms. Their mouth is situated on the underside and their anus on top (except feather stars, sea cucumbers and some urchins).
tentacle-like structures called tube feet with suction pads situated at their extremities. These tube feet are hydraulically controlled by their vascular system, which supplies water through canals of small muscular tubes to the tube feet. As the tube feet press against a moving object, water is withdrawn from them, resulting in a suction effect. When water returns to the canals, suction is released. The resulting speed of these animals are generally very slow.