Sea Stars, Sea Urchins and Related Animals

Echinoderms are a group of closely related animals that includes starfish, brittlestars, featherstars, sea urchins and sea cucumbers; "echinoderm" means literally "spiny skin". These highly evolved invertebrates are unique in possessing "pentaradiate" or five-part symmetry as adults, an hydraulic water vascular system that aids in locomotion, and a remarkable ability to regenerate lost body parts.