Endoskeleton of echinoderms is unique as mesodcrmal. It consists of numerous ossicles secreted by dermis and lodged in its outer region. Echinoderms have almost universally adapted and retained pentamerous radial symmetry. Their radial symmetry secondarily evolved since echinoderms are supposed to have been derived from bilaterally symmetrical ancestors. In the indirect development various type of free swimming larvae are formed. Echinoderm larva is strinldngly bilaterally symmetrical contrast to adult. Water vascuiar system is the characteristic feature of echinoderms. It is a division of coelom and system of canals and apandages of body wall. It is also termed as ambulacral system.