Starfish are fairly rare as fossils and belong to the same group (the echinoderms) as sea urchins and crinoids. They date back to the beginning of the Palaeozoic era and can be regarded as "living fossils", having remained virtually the same for 480 million years.

The body usually has five arms, and has at its centre, on the underside, a mouth. Starfish are predators, and can push out their stomachs through their mouths, catch food and digest it outside the body. They are also known to open mollusc shells.

Fossils are usually only fragments, which can be quite difficult to identify. In England, Ordovician slate sometimes yields starfish of the genus Siluraster, whose body measures 5 cm across.

See also: blastoids
See also: brittle stars
See also: sea lilies
See also: sea urchins

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