• Norwegian: sjøstjerner


The popular names sea star or starfish have a rather obvious origin. The star-shaped body consist of a central disk, including a mouth and a stomach. The disk is surrounded by a number of hydraulically driven arms. A five arm configuration is perhaps the most common, but there are plenty of exceptions. The C. papposus may have as many as 16 arms. Every arm includes a hydraulic system where water is pumped around to extract and contract the arm. If an arm is lost, it can be regenerated. As long as the central disk is intact, there is a god chance the sea star will survive, depending on the food access while waiting for the new arm to grow.

Sea stars feed on mussels, snails, many bristled worms and even other echinoderms. The mouth is positioned under the disk. On the tip of each arm there are light sensitive organs acting almost as eyes. Sea stars have a rather complex nervous system, but lack a central brain.

The sea stars exhibit a complex life cycle including a stage as a planktonic larva. It floats around for some days or weeks, feeding on smaller planktonic organisms, before it settles down on the sea bed.


The class of sea stars form the subphylum Asterozoa, together with the brittle stars (Ophiuroidea). The seven orders of sea stars include more than 2000 species worldwide, 43 of them are registered in Norway.