Echinoderms live exclusively in the sea. The phylum Echinodermata, meaning "spiny skin," consists of roughly 6,000 species. It is the largest phylum with no freshwater or terrestrial members, according to Encyclopedia of Life.
Members of the phylum include sand dollars, sea urchins, sea cucumbers, starfish and sea lilies. The invertebrates are found in all the world's oceans and at all depths, with most moving across the sea floor through vascular structures known as tube feet. While larvae may have bilateral symmetry, adults are radially symmetric, with appendages pointing outward from the center of the body. Many echinoderms have the ability to regenerate, or grow new limbs that are lost from attacks by predators. The echinoderm diet consists of barnacles, clams, mussels, snails, sea urchins and a variety of other small organisms.