Normally 10-30cm. Maximum diameter 50cm. Starfish are unmistakable with their five arms with rows of tube feet on the underside. The central mouth of the starfish is underneath the upper body. The common starfish is orange in colour and is occasionally seen with missing arms. Distribution
They are abundant in the Atlantic ocean, and are found occasionally in the Mediterranean, although it is not native here.
Starfish can be found in rock pools and on beaches. The habitat varies and includes coarse and shelly gravel and rock. Abundance increases markedly on algal carpets as compared with fine sand. The common starfish is unusual in that it tolerates estuarine habitats. Its habitat range extends offshore for 400m.
Common starfish feed on mussels, crustaceans, worms and echinoderms (starfish or sea urchins).
Starfish are propelled very slowly along the sea floor by their tiny tube feet. Tube feet can produce strong suction, fixing the starfish in place and making it difficult for a predator to eat the entire organism. Occasionally starfish can be seen with missing limbs. This is not a great loss for a starfish as they can grow them back. Sometimes common starfish with six or more limbs are seen, this may be a result of the starfish accidentally growing two limbs to replace a single loss.
Starfish are active carnivores, and scavenge too. They prey on bivalve molluscs by forcing their shells open with their tube-feet. The stomach everts over or into the prey liquefying it so that it can be easily digested. In shallow waters dense congregations of starfish can be found over an expanse of several kilometres.
Females release their eggs into the sea and the males respond to this by releasing sperm into the sea. Fertilisation happens externally. A single female is capable of releasing up to 2.5 million eggs. Fertilised eggs develop into larvae which are able to swim about. These larvae swim for about three weeks before settling and beginning metamorphosis into the more familiar and sedentary starfish.