Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea. Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or “basket stars”
The common starfish normally has five arms, broad at their base and gradually tapering to a point at their tips, which are often turned up slightly. There is a line of short white spines running along the centre of the aboral (upper) surface of the arms with low, soft mounds called papulae on either side. The oral (lower) surfaces of the arms have rows of small tube feet, used in locomotion and feeding. The starfish is usually orange or brick red on the aboral surface and paler on the oral surface but can also be purple or pale brown. Individuals from deep water are usually paler. It grows to a maximum diameter of about 52 centimetres (20 in) but a more normal size is 10 to 30 cm (4 to 12 in).
The fossil record for starfish is ancient, dating back to the Ordovician around 450 million years ago, but it is rather poor, as starfish tend to disintegrate after death. Only the ossicles and spines of the animal are likely to be preserved, making remains hard to locate. With their appealing symmetrical shape, starfish have played a part in literature, legend, design and popular culture. They are sometimes collected as curios, used in design or as logos, and in some cultures, despite possible toxicity, they are eaten.
