Indian Echinoderms their resources biodiversity zoogeography and conservation

Echinoderms are an interesting groupof animals distributed only in the seas since they do not have osmoregulatory powers to adjust to lower salinities. They are truly stenohaline animals. At present there are 7000 living species.Their fossil history is well documented due to hard parts except in case of sea cucumbers. Nearly 13,000 species of fossils are known. They have two unique features among the invertebrates: an internal water vascular system which is operated hydraulically opening to the exterior by a perforated plate known as madreporite and the presence of tube-feet which are extension of water vascular system.