Or seastar; Any echinoderm of the subclass Asteroidea with arms radiating from a central body. Usually there are five arms, but some species have more. They are covered with spines and small pincerlike organs. There are also a number of small tubular processes on the skin surface that assist in locomotion and respiration. Starfish are predators, and vary in size from 1.2 cm/0.5 in to 90 cm/3 ft. /> Some species use their suckered tube feet to pull open the shells of bivalve mollusks, then evert their stomach to surround and digest the animal inside. The poisonous and predatory crown-of-thorns of the Pacific is very destructive to coral and severely damaged Australia’s Great Barrier Reef when it multiplied prolifically in the 1960–70s, but by 1990 it had itself practically disappeared, perhaps because of attack by parasites. Another destructive species, Asteria amurensis, spread round the coast of Tasmania 1993, and could reach as far as Sydney. It is normally found only in the northern Pacific and was probably introduced into Tasmania in the ballast water of a ship traveling from Japan.Echinoderms characterized by five arms extending from a central disk; SYN. sea star. star-fish