Definition of: echinoderm

(i·kī′nə·dûrm) noun
Any of a phylum (Echinodermata) of coelomate, bottom-dwelling marine animals, as starfishes, sea cucumbers, etc., characterized by pentamerous radial symmetry, a skeleton of calcite plates just beneath the skin, and a water-vascular system which serves primarily for locomotion.
—e·chi′no·der′ma·tous (-dûr′mə·təs), e·chi′no·der′mal adjective