Probably the most colourful animals of the intertidal pools are the Eight-armed Seastars which grow to about 50mm across. In spite of the name some individuals may have more or less than eight arms. Their colours are genetically determined and the variety of patterns is astounding. Each seastar usually has a number of hues. Since the Eight-armed Seastar likes company, a single rock pool can have dozens of animals, no two of which are alike. You would think that this would make them very obvious but the seastars are surprisingly well camouflaged. They are usually found in pools and wet crevices near the low tide mark where they blend in with growths on the rocks.

The Eight-armed Seastar has a number of aliases, perhaps because it is so common and widespread. Other names include the Carpet, Common, Cushion and Spurred Seastar. Even its scientific name has changed lately as marine biologists learn more about its relationship to other seastars. It is now called (Meridiastra calcar) but you will find it’s still called (Patiriella calcar) in most reference books.

Seastars have a top and bottom but not a front and back. The mouth is on the underside and the very important water inlet (madreporite) is near the centre of the top. Seastars move by hydraulically operated tube feet which are connected to a network of water-filled “pipes” from the inlet and which often end in suckers.

Despite not having a head a seastar knows which way is up and if turned over it will start bending some of its arms and pulling with the tube feet in those arms until it rights itself. The tube feet also help hold on to the animal’s food.

Eight-armed Seastars eat just about anything they can get their feet on. Algae, encrusting organisms, animal remains and detritus are all on the menu. The seastar protrudes its stomach through its mouth to envelop the food and begin digestion.

The animals are either male or female. They spawn from about August to November, releasing eggs and sperm into the sea. Fertilisation takes place there and the larvae go through several stages for about 10 days before settling on the rocks and changing into tiny seastars. During their time in the plankton the larvae can be dispersed over a wide area by the East Australian Current and its eddies.