Class Asteroidea, starfish and sea stars 2, 1

The Common starfish, Asterias rubens

Common starfish, Asterias rubens

The Common starfish Asterias rubens, above, is found is found in the North Atlantic and North Sea coasts down to about 400 m, often in mussel beds and amongst barnacle encrustations. It can grow up to 52 cm in diameter, but more usually 10 - 30 cm. Its colour varies from brown to orange and also violet; the deeper dwelling individuals tend to be paler. When active the tips of its arms are often curled up. Movement is slow at around 15 cm a minute.

It can detect its prey by smell, and prey includes bivalves, polychaete worms, barnacles, marine snails and other echinoderms. It can pull open a mussel using the suckers on the undersides of its arms. With a gap of just 1 mm it inserts a fold of its stomach which secretes enzymes and starts the digestive process. When the prey has been sufficiently liquefied it removes its stomach with the prey soup inside.

Life span is thought to be about 7 or 8 years. And a female can release around 2.5 million eggs in one go.

Spiny starfish, Marthasterias glacialis

Spiny starfish, Marthasterias glacialis

The Spiny starfish, Marthasterias glacialis, above, can be found in the North East Atlantic and the Mediterranean in rock pools and down as far as 200 m deep. Fully grown specimens can be as large as 30 cm across, and there have been a few individuals reaching 75 cm, making it the largest starfish in British waters! It has 3 rows of spines running down each arm. Its colour varies widely and includes grey, green, blue, brown and pink.

Spiny starfish are predacious, with bivalves, crustaceans and fish, either dead or alive forming most of their diet. They have light-sensitive organs a the tip of their arms, and this explains the frequently observed behaviour of them raising their arm tips.

Labidaster annulatus

Starfish Labidaster annulatus

Labidaster annulatus above, can be found in the Antarctic ocean and is a type of starfish called a Sun star. It is unusual in that it has forked arms, and can grow up to 50 centimetres across. It will eat almost anything.

Goniaster tessellatus and Tosia australis

Starfish Gonaster tessellatus

Goniaster tessellatus (above) can be found in the tropical Atlantic.

Tosia australis, as its name suggests, can be found in Australian waters where it is fairly common from intertidal to 40 metres deep in the open or under rocks. Its common name is the Biscuit star, and it is easy to see why. It reaches about 10 centimetres in diameter.

Reticulated sea star, Oreaster reticulatus

Reticulated sea star, red cushion sea star, West Indian sea star

The Reticulated sea star, Oreaster reticulatus, above, has at least three common names, the Reticulated sea star, the Red cushion sea star, and the West Indian sea star. It can grow up to 50 cm in diameter. The colour of the adult can vary and be red, orange, yellow or brown. The juveniles are greenish brown. The sexes are separate, and large numbers gather together at breeding time, otherwise it is solitary. It is found in the Western Atlantic on sandy bottoms and coral up to 37 metres deep, where it feeds on algae, sponges and small invertebrates. To feed it pulls together a pile of sediment, turns its stomach inside out to enclose the pile, eats what is edible and ejects the rest.