A curious inhabitant of the sea floor, starfish or sea stars are not fish but star-shaped echinoderms of the class Asteroidea (with sea urchins, sand dollars, and basket stars as relatives). There are some 1500-2000 species of starfish inhabiting all of the world's oceans with the greatest diversity occurring in shallow areas and reefs. They can exhibit different numbers of arms and display various coloration and body shapes. Starfish are slow-moving, though some species can move more than 2 meters per minute. They feed primarily on gastropods, arthropods, bivalves organic matter, and corals.