Starfish eat sponges, ascidians and organic debris, some can use their arms to open bivalves molluscs . Their mouth is underneath and their anus on top .The two are connected by the stomach and intestines. Starfish evert their stomachs and digest their prey outside of their bodies.

Different species of starfish employ different reproductive strategies. Some can split into two, some cold water species are viviparous others species are hermaphrodite. in most cases, however, sexes are usually separate and the gonads are on the arms. Most reproduce by releasing eggs or sperm into the water when other starfish are nearby. The fertilised eggs spend time in the water column as bilaterally symmetrical individuals before settling and changing shape into little stars.

Starfish and other echinoderms are unusual in that they rarely have barnacles growing on them. They are kept free from lodgers by the pedicellaria, minute jaw-like structures on the upper surface. The touch of settling barnacle larvae will cause the pedicellaria grab at the intruders. Whist the upper surface is kept clear, small shrimps, snails and brittlestars can be found living on the underside of starfish.

Starfish are not generally harmful to people, the notable exception being the crown of thorns which is barbed and poisonous