Movement & Response

Echinoderms have many tube feet on each of their "arms" and with the combination of the water vascular system, it makes up the movement of echinoderms. By expanding and contracting certain chambers in the water system, it moves the water into certain feet and that allows the muscle to extend which makes the feet retract. When the echinoderms expand and contract the correct tube feet in proper order, it allows walking to occur. In sea stars which belong to the class Asteroidea, there is a muscular pump that squeezes water out of the tube feet and that causes it to extend and straighten. Also in the class Ophiuroidea, which includes brittle stars, their tube feet are pointed without the suction movement, so they manouver around by rowing their "arms".
Echinoderms do not have anything known as a brain or any type of cephalization. They only have a nerve ring surrounding their mouth which then extends a series of nerve networks towards each of the body's region. In some echinoderms, ganglia is also present along the nerve networks. With the nerve ring, it allows the echinoderm to track down food around them. In addition to the nerve ring, echinoderms have ocelli which are like "eyes" located at the tips of the arms and they are light sensitive cells that alert the echinoderm if they are in light or dark areas. Also the sense organ, statocyst, helps with the echinoderm to determine the position the organism is in in relation to being upright or upside-down. These sensory organs are what makes up the echinoderms' nervous system.