Starfish exhibit several unique adaptations that enable them to survive in the world’s oceans, including radially symmetrical bodies, unique tube feet that permit movement and the ability to regenerate lost arms. About 2,000 different starfish species inhabit the oceans, and while each has adapted to its unique surroundings, they all exhibit these three adaptations.
Radial symmetry means the starfish are symmetrical with respect to a central point. Most starfish have five arms that radiate out from their central body, but some species have up to 40 arms. The mouth of starfish resides underneath the center of their bodies. On the ventral side of their arms, starfish have hundreds of tiny tubular structures filled with seawater. They use these feet for locomotion and capturing and holding on to prey.
One of the most unusual adaptations of starfish is their ability to evert their stomachs. When a starfish captures a clam or similar bivalve, it grips it with its arms and pries it open slightly. Then, the starfish everts its stomach, sliding it into the shell of the prey. The stomach then digests the prey and retracts back into its original form.
Additionally, starfish have evolved a tough, spiked covering for their dorsal sides, which helps to protect them from predators. The protective covering is composed primarily of calcium carbonate.