Starfish require an established medium to large aquarium system that has been running at least 6 months. Starfish graze on micro film on the rocks all day everyday and are prone to starving in small tanks and newer tanks as the microfauna runs out faster then it can regrow.
Most starfish have five arms that radiate from a central disc, but the number varies with the group. Some species have six or seven arms and others have 10–15 arms.The Antarctic Labidiaster annulatus can have over fifty. Having descended from bilateral organisms, starfish move in a bilateral fashion, with certain arms acting like the front of the animal.
The gut of a starfish occupies most of the disc and extends into the arms. The mouth is located in the centre of the oral surface, where it is surrounded by a tough peristomial membrane and closed with a sphincter. The mouth opens through a short oesophagus into a stomach divided by a constriction into a larger, eversible cardiac portion and a smaller pyloric portion. The cardiac stomach is glandular and pouched, and is supported by ligaments attached to ossicles in the arms so it can be pulled back into position after it has been everted.
