A common starfish is instantly recognizable by his radial shape, often five arms spaced out from a central body. With more than 1,800 species of starfish, you can find the right size and type to match your saltwater aquarium environment. Keep an eye on your starfish when it loses a limb -- the result might surprise you.
Starfish are unique among aquatic life because they have the ability to regenerate an arm when they lose one. It's not unusual for a predator to bite off part of an arm, and some species of starfish can break off their own arms where it connects to the central body to help escape from predators. It usually takes about a year to completely grow back. Although some species of crab, such as the stone crab, can break off their own claws and grow them back, they can't grow back any other body parts, such as legs. Also, crabs grow back their claws over long periods of time, adding size every time they molt off their exoskeletons. Starfish aren't confined to growing new appendages during certain times of the year; regeneration is a continual process once a starfish loses an arm.
An amazing thing can happen when a starfish loses a limb -- if it's not eaten by a predator, that is. Starfish are capable of asexual reproduction, which means one starfish can create another one without mating. In this case, a severed limb can become an entire body, producing an entirely new starfish. Some species of starfish can detach their own arms without injury with the intention of reproducing.
How They Move
Starfish don't swim like fish do. Instead, as echinoderms, they use hundreds of tiny tube feet on the bottom of each arm to move around. Instead of blood, a starfish uses sea water as its vascular system. It pumps water into its body and into the feet tubes. Muscles in its arms push water into certain tubes to engage the suction cups on the bottom, then relax to release the water and the suction cups. By pushing water into the tube feet in a rippling effect along its arms, a starfish is able to grip and release rocks, coral or the sand and pull itself forward. The tube feet also allow starfish to grab tight to their prey.
Although it's unlikely to be a problem in a home aquarium, the starfish's ability to regenerate and reproduce asexually causes a problem in the commercial mollusk industry. Starfish love to eat the mollusks, which cuts down on the fishermen's catch. At one point, mollusk fishermen would cut caught starfish into pieces to kill them, then toss the pieces into the water. However, that didn't kill the starfish. Instead, cut up starfish pieces became starfish. The practice of cutting starfish into pieces caused many reef areas became overpopulated. This is still a problem in some areas.
starfish image by Christopher Meder from Fotolia.com