The fish bowl dating
About 1,500 species of starfish occur on the seabed in all the world's oceans, from the tropics to frigid polar waters.
They are found from the intertidal zone down to abyssal depths, 6,000 m (20,000 ft) below the surface. They typically have a central disc and five arms, though some species have a larger number of arms.
The larvae of echinoderms have bilateral symmetry, but during metamorphosis this is replaced with radial symmetry, typically pentameric.
Starfish are included in the subphylum Asterozoa, the characteristics of which include a flattened, star-shaped body as adults consisting of a central disc and multiple radiating arms.
The subphylum includes the two classes of Asteroidea, the starfish, and Ophiuroidea, the brittle stars and basket stars.
Asteroids have broad-based arms with skeletal support provided by calcareous plates in the body wall Most starfish have five arms that radiate from a central disc, but the number varies with the group.
The edges of adjacent paxillae meet to form a false cuticle with a water cavity beneath in which the madreporite and delicate gill structures are protected.
Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or "basket stars".
Pedicellariae are compound ossicles with forceps-like jaws.
They remove debris from the body surface and wave around on flexible stalks in response to physical or chemical stimuli while continually making biting movements. Paxillae are umbrella-like structures found on starfish that live buried in sediment.
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.