starfish

The sun star, a spiny starfish of the order spinulosa. The sun star is one of those less common starfish that have more than five arms: it has twelve. One species of starfish which lives in the waters off South America has no fewer than 44 arms. It is not clear whether the extra arms assist in its predatory activities, and they may increase its vulnerability to attack or damage.

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 molluscs, 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 1960s–70s. Although it had practically disappeared by 1990, in 1996 another outbreak along the Great Barrier Reef was officially declared.

Another destructive species, Asteria amurensis, spread round the coast of Tasmania in 1993, and could reach as far as Sydney. It is normally found only in the North Pacific and was probably introduced into Tasmania in the ballast water of a ship travelling from Japan.