Unlike many sea creatures, starfish, also called sea stars, don't have gills or fins. In fact, they don't even have brains, hearts or blood. What they do have, however, is several specialized adaptations that allow them to survive in a constantly changing and dangerous environment filled with predators.
If a starfish loses an arm, an organ or even most of his body, he can regrow whatever part he needs as long as part of the central ring is intact. Thanks to this ability, if a predator attacks and manages to take a bite, a starfish won't bleed to death, get an infection or be permanently crippled. In fact, one starfish may become two if part of the central ring is attached to the part separated from the main body. Some starfish intentionally reproduce this way, by separating their own bodies in half, if the population is dwindling.
A starfish can eat anything he can fit in one of his two stomachs. He does this by pushing a stomach out of his body where it can safely digest large prey, like an oyster, and then pulls it back into his body after the food is mostly digested. The ability to eat prey of varying sizes is an advantageous adaptation for the starfish.
A starfish's arms are covered with hundreds of small suckerlike feet. These feet not only help him walk but give him strength to pry open shelled prey like clams and oysters. Since a starfish moves so slowly, he relies heavily on prey that doesn't move. The tube feet also help keep him anchored in place, such as on a rock, coral branch or the ocean floor, during a storm and against tide forces and ocean currents.
What passes for a starfish's circulatory system uses ocean water instead of blood. This is essentially a series of tubes that extend from the stomach to the arms to transport nutrients. A starfish doesn't have a heart, but water running through the arms and feet provides oxygen.