Starfish are star-shaped echinoderms. There are about 1,500 species of starfish in all the world's oceans, from the tropics to frigid polar waters. Starfish are marine invertebrates. They typically have a central disc and five arms. The upper surface may be smooth, granular or spiny. Many species are brightly colored in various shades of red or orange, while others are blue, grey or brown. Starfish have tube feet and a mouth at the centre of the lower surface. They are opportunistic feeders but usually feed on smaller invertebrates. Most can regenerate damaged parts or lost arms and they can shed arms as a means of defense.
Fossils of starfish have been found from 450 million years ago. With their appealing symmetrical shape, starfish have played a part in literature, legend, design and popular culture.