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The term Echinodermata (Gr., echinos= spiny, derma=skin), was coined by Jacob Klein Echinoderms are triploblastic, radially symmetrical (adult) often pentamerous, larva with bilateral symmetry, sessile or creeping at bottoms. Echinoderms are exclusively marine deuterostomes. All echinoderms are benthic ; bottom dwellers (except few pelagic sea cucumbers), mostly free living except sea lilies. Spiny skinned; enterocoelic coelomate; organ system grade of organization; gregarious Body is unsegmented Echinoderms are uncephalized (head absent), body parts organized about an oral-aboral axis. Endoskeleton (mesodermal origin) is composed of unique calcareous ossicle bearing protective spines. Digestive tract is complete except Brittle star. An outstanding characteristics is echinoderm is their complex coelom (enterocoel) and its ambulacral system, derivatives; the water vascular system , perivisceral coelom and haemal system. Locomotion by contractile appendages of ambulacral system/ water vascular system called tube feet. Tube feet consists of ampulla, podium and sucker. It also serves for respiration and food capture. Presence of pinna like structure called pedicellariae that protects the skin gills. Excretory system is absent. Nervous system is diffused decentralized, usually consisting of nerve net, nerve ring and radial nerves, but no brain. Sense organs are poorly developed and consists of tactile tentacles, pigment eye spots and statocysts. Respiration by Dermal branchiae or papulae (star fish), gills (sea urchin), genital bursae(brittle star), cloacal respiratory tree (sea cucumber). Circulatory system is open type : heart absent. Blood does not contain respiratory pigment. Mostly dioecious, copulation absent, fertilization external. Eggs are homolecithal (yolk uniformly distributed in egg) Cleavage is radial and indeterminate Development is indirect through free swimming larval stages.