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,
Asexual reproduction in starfish fission. In Brazil, only male individuals have been found and fission takes place all the year round, though primarily in the winter. Fission seems to be correlated with certain stress factors such as particularly low tides, when many starfish may be exposed to the air. "Nepanthia belcheri" has a variable number of arms and divides by fission in a similar manner. It is a hermaphrodite, some individuals having gonads that function as testes and others gonads that function as ovaries. After fission, the gonads regress and individuals that previously had mature female gonads become masculinized, developing male-type gonads. Many larger