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.
This fact was discovered by fishers who used to cut them in half to kill them, only to find twice as many starfish growing new legs the following year. Each arm has a pair of sexual organs, or gonads. Pores in the arm release eggs or sperm into the water during the first days of spring. Sometimes starfish will gather together in sexual aggregations to improve the odds of successful fertilization. The embryo will pass through different larval stages before it changes, or metamorphoses, into a tiny replica of its parents.