Starfish Starfish Starfish or sea stars are star-shaped echinoderms belonging to the class Asteroidea. Common usage frequently finds these names being also applied to ophiuroids, which are correctly referred to as brittle stars or "basket stars". About 1,500 species of starfish occur on the seabed in all the world's oceans, from the tropics to frigid polar waters. They are found from the intertidal zone down to abyssal depths, below the surface. Starfish are marine invertebrates. They typically have a central disc and five arms, though some species have a larger number of arms. The aboral or upper surface may be smooth,
Reef starfish or three months of their placement, while the mussels expanded within six months to cover 20-30% of the low zone when "S. australis" was removed. Without their predation, the mussels overwhelmed the area, threatening biodiversity. The juveniles of the species are detritivores. Reef starfish Reef starfish (Stichaster australis) is a species of starfish found in the South Pacific Ocean around New Zealand. A keystone species, the carnivorous starfish plays an important part in reducing the expansion of mussels. "S. australis" is pink or purple in color, with 11 arms. Found throughout New Zealand, "S. australis" is a keystone species in