How Come: the strange ways of starfish

A fish shaped like a cartoon star: What's not to love? But while the name "starfish" has been popular for centuries, scientists prefer an alternate name: sea star.

Why? Star fish aren't fish. The many-armed creatures are close relatives of spiny sea urchins and cookie-shaped sand dollars, with similar bony, calcium-rich exteriors. (All three are echinoderms, from Greek words for "hedgehog skin.") Sea stars hang out in seawater from shallow tide pools to ocean depths four miles down.

And like lions and tigers and bears, sea stars are predators, saltwater carnivores fond of the same shellfish (like clams and oysters) eaten by humans. But while hungry humans belly up to a clam bar, starving sea stars perform a feat that's literally stomach-turning.

Imagine your dinner is hidden inside a tightly closed oyster shell. No problem for a typical sea star, who uses his suction-cuplike feet to pry the shell open a crack.

Open shell, insert . . . oyster spoon? Seafood fork? Stomach? Wait, what? Yep, the sea star spits one of his (two) stomachs through the opening. The invading stomach oozes over the oyster, and begins to digest it whole -- like a spider spitting digestive juices on a web-trapped fly. The sea star pulls his mollusk-full stomach back into his mouth, and dinner is served.

Such feats are performed by sea stars belonging to nearly 2,000 different species -- red or orange or purple or beige, solid-colored or wildly patterned; with five arms (or rays) or six, or 20, or even 50.

At the end of each arm is a small, light-sensing eye. Sea stars move using hundreds or thousands of tube feet ("podia"), which run in rows along their arms. The tubes are filled with seawater, streaming through canals in the sea star's body. By increasing water pressure to the tubes, a starfish swells its many feet, latching on to a surface in caterpillarlike waves.

If an arm is severely injured -- or even deliberately detached by a star escaping some peril -- the missing part can be regrown over the course of a year. Remarkably, some species can replace their entire body from a single leftover arm.

Scientists don't know how they do it. But by studying sea stars, researchers hope to unravel the mysteries of healing and tissue regeneration in humans and other animals.

Watch a time-lapse video of how a sea star moves at http:// vimeo.com/370098. View sea stars in a stunning variety of colors and patterns at http:// www.ryanphotographic.com/ asteroidea.htm.