The skins of these creatures are filled with hard plates or spines and most have the body divided into 5 or more radial parts, each with duplicate internal organs.

Movement is achieved with hundreds of tiny hollow tubes, which are extended by pumping sea water into them.

Members of this group can regrow lost body parts, with some being able to grow a fragment into a new individual.

Sea stars can be either male or female. The anus of a sea star is in the centre of its upper side, and its mouth opens at the centre of the underside. The tube feet, which mostly end in suckers, are set in grooves along the undersides of the arms.

They have tiny white gills in which they use to filter oxygen from the surrounding water.

Tiny snapping pincers, called pedicellariae, grow on the upper surfaces of some ot these echinoderms. These pedicellariae keep the skin free of debris and small creatures.

Sea stars are carnivores, feeding on sponges, bryozoans, bivalves, worms and crustaceans. Some species eat decaying particles found on rocks, sand and seaweed.

A sea star will gradually pull apart a bivalve's shell with its feet. Then it pushes out its stomach and surrounds the soft parts of the mollusc with its digestive organs. When the meal is eaten, the stomach is pulled back into the body.

Usually found below the low tide water mark on the bottom around rocks and corals and are between 8-50 cm in diameter.