Star fish , sea urchins , and their relatives ( including feather stars , brittle stars , basket stars , sea daisies , sea lilies , and sea sea cucumber ) make up the phylumn Echinodermata . a unique feature of echinoberms is the water vascular system , which consist of a series of water – filled canals from which protrude thousand of tiny tube feet . The tube feet may be used for movement , feeding , respiration . Other features include pentaradiate symmetry ( that is , the body can be divide into five parts radiating from the centre ) no heads ; diffuse , decentralized nervous system that lack a brain ; and no excretory organs . Typically , echinodrems also have an endoskelton ( internal skeleton ) consisting of hard calcite ossicles embedded in the body wall and often bearing protruding spines or tuberless . The ossicles may fit together to form a test ( as in sea urchins ) or remain seprate ( asin sea cucumbers ) .