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Sea Stars

You may call them starfish, but don’t let the name fool you. Sea stars are not fish. They’re echinoderms, spiny-skinned animals that are shaped like a wheel. Instead of fins, sea stars have arms—five or more, depending on the species—radiating from a central disk.

You might recall finding a sea star on the beach, your skin tickling as it slowly crept around. Each arm contains rows of teeny, supple tube feet that are operated by a hydraulic system. Intricate canals draw in water and channel it to the feet, enabling them to extend. Suction cups on the bottom help the sea star move with a grip-and-pull action. If a sea star finds itself upside down, it can rotate one arm and pull itself over.

A sea star can drop an arm if a predator grabs it. Incredibly, however, the arm can regenerate—and, in some species, a single arm with a bit of the central disk can sprout a whole new animal. This process takes about a year.

Sea stars will eat just about anything they can get their hands—er, feet—onto. A sea star’s mouth is located on its underside, right in the middle of its central disk. If the food of choice is bigger than the mouth, the sea star will flip its stomach out, secrete a digestive enzyme that purées the prey, absorb the goop, then withdraw the stomach and slip away without leaving a trace.

With about 1,800 species, sea stars come in a dazzling array of colors and can range in size from a small bug to a large clock. You'll find sea stars shining in the Oceans gallery of Waters of the World, in the Abbott Oceanarium and in a touch pool in Polar Play Zone.

 

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