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With their appealing symmetrical shape, starfish have played a part in literature, legend, design and popular culture.

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The Asteroidea occupy several significant ecological roles.Starfish have tube feet operated by a hydraulic system and a mouth at the centre of the oral or lower surface.They are opportunistic feeders and are mostly predators on benthic invertebrates.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.The water vascular system of the starfish is a hydraulic system made up of a network of fluid-filled canals and is concerned with locomotion, adhesion, food manipulation and gas exchange.

Water enters the system through the madreporite, a porous, often conspicuous, sieve-like ossicle on the aboral surface.

The structures are supported by collagen fibres set at right angles to each other and arranged in a three-dimensional web with the ossicles and papulae in the interstices.

This arrangement enables both easy flexion of the arms by the starfish and the rapid onset of stiffness and rigidity required for actions performed under stress.

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.

These are honeycombed structures composed of calcite microcrystals arranged in a lattice.