The members of phylum Echinodermata are spiny-bodied sea creatures which possess an endoskeleton (internal skeleton) composed of calcareous ossicles (small bones), embedded in the skin. Echinoderms are exclusively marine, bottom-dwelling and free-living animals. They are triploblastic coelomates, which have an organ-system level of organization and unsegmented bodies. The adult forms are radially symmetrical, while their larvae are bilaterally symmetrical. This characteristic makes echinoderms unique as the larvae show an advanced symmetry (bilateral) as compared to the adults, which show a more primitive form of the feature (radial). The latter exhibit a pentamerous radial symmetry and their body parts are arranged along five different axes. The body shape of adult echinoderms varies from star-like (starfishes or sea stars) to globular or globe-like (sea urchins) to cylindrical (sea cucumbers).
Examples of echinoderms: Asterias (Starfish), Echinus (Sea urchin), Antedon (Sea lily), Cucumaria (sea cucumber), and Ophiura (Brittle star).