Starfish belong to the phylum Echinodermata. The phylum name means "spiny skin" in Greek. All echinoderms are marine invertebrates with radial symmetry and water vascular systems that allow locomotion.
There are about 1,500 species of starfish distributed throughout the world's oceans. They live from the intertidal zone down to depths of 20,000 feet. Most starfish prey on other invertebrates living on the seabed, but some species eat algae and decomposing organic matter. In turn, they serve as food for gulls, sea otters, predatory marine snails, crabs, fish and other starfish. Starfish are keystone species that determine the types and numbers of other species in their ecological communities.