any of a phylum (Echinodermata) of marine animals with a water-vascular system, and usually with a hard, spiny skeleton and radial body, including the starfishes and sea urchins
Any of numerous radially symmetrical marine invertebrates of the phylum Echinodermata, which includes the starfishes, sea urchins, and sea cucumbers, having an internal calcareous skeleton and often covered with spines.