There are some 2,000 species of sea star living in all the world’s oceans, from tropical habitats to the cold seafloor, most often near rocky shores. The five-arm varieties are the most common, hence their name, but species with 10, 20, and even 40 arms exist. Many species are brightly colored in various shades of red, orange and pink, while others are blue, grey or brown.
Beyond their distinctive shape, sea stars are famous for their ability to regenerate limbs, and in some cases, entire bodies. They accomplish this by housing most or all of their vital organs in their arms. Some require the central body to be intact to regenerate, but a few species can grow an entirely new sea star just from a portion of a severed limb.
They use sea water instead of blood to pump nutrients throughout their bodies.
Sea stars don’t have eyes as people. They have eyespots at the tips of their arms. Eyespots help a sea star when it is out of the water, the sea star may end up on the beach at low tide. If it stays in the sun too long the body would dry out causing its death. Using the eyespot, the sea star can find its way to a shade so it can stay cool and damp until the water level rises again at high tide.
Most sea stars do not care for their young, the female just releases the eggs into the water and the larvae grow up on their own. In some species, females do care for their young; those mothers protect their eggs beneath their bodies. They guard the larvae until they are big enough to go off on their own.
Despite of their name, starfish are not fish, it’s an echinoderm, a type of marine animal that is spiny-skinned.