Common starfish Common starfish The common starfish or common sea star ("Asterias rubens") is the most common and familiar starfish in the north-east Atlantic. Belonging to the family Asteriidae, it has five arms and usually grows to between 10–30 cm across, although larger specimens (up to 52 cm across) are known. The common starfish is usually orange or brown, and sometimes violet; deep-water specimens are pale. The common starfish is to be found on rocky and gravelly substrates where it feeds on molluscs and other benthic invertebrates. The common starfish normally has five arms, broad at their base and gradually tapering to
Crown-of-thorns starfish a week or more. The spines, which are brittle, may also break off and become embedded in the tissue where they must be removed surgically. Saponins seem to occur throughout the lifecycle of the crown-of-thorns starfish. The saponins in the eggs are similar to those in the adult tissues, and presumably these carry over to the larvae. The mouthing behaviour of predators of juvenile starfish with rejection suggests the juveniles contain saponins. The adult crown-of-thorns is a corallivorous predator that usually preys on reef coral polyps. It climbs onto a section of living coral colony using the large number of