Starfish have a very simple body structure with five or more legs in a radial array around a central body disk. Each leg has paired rows of small tube feet in a groove on the bottom of each leg. The tube feet are used for locomotion and feeding. They are tipped with a small suction cup which can be extended or withdrawn to move the starfish over the sea bottom. While most starfish travel at speeds measured in inches per hour, the giant sunflower stars have been observed galloping along at nearly 2 feet a minute.
Tube feet make the starfish the nemesis of clams and other slow moving mollusks.
Imagine ten thousand powerful suction cups pulling relentlessly on the valves of a clam's shell. There is no escape as the vacuum-like action relentlessly pries open the clam's only defense. Once the clam's muscles relax, the starfish extrudes its stomach through its mouth into the clam's shell and digests the mollusk's soft body. Although clams are often the favorite prey of starfish, some varieties prefer to feed on plankton, or even dead marine organisms. Starfish have the ability to regenerate lost arms or body parts.