RESPONSE AND MOVEMENT

Echinoderms have a very uncomplicated nervous system. Most species have a nerve ring that surrounds the mouth with radial nerves that connect the central ring to other parts of the body. Some echinoderms also have sensory cells that recognize chemicals released by potential prey. Sea stars also have up to 200 light sensitive eye spots on the end of each arm able to detect whether they are in light or dark. Star fish and other echinoderms also have statocysts which tell the animal if it is upside down. Most echinoderms are motile except for sea lillies and feather stars who attach to rocks. Echinoderms use tube and thin layers of muscle latched onto plates of the endoskelton to move around. With the pumping of water in and out of the water vascular system the tube feet act as suction cups and make it extremely hard to move a sea star from where it is. To protect themselves from predators echinoderms have numerous defenses. Sea urchins have tons of long spikes (sometimes containing poison) which help to keep enemies away. Others, like the sand dollar, burrow away in the sand and mud where as the brittle stars shed a leg whenever they feel a predator close.