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SEA STARS: BEAUTY AND BEAST

AUBURN, MARCH 24, 2000---Most people at one time or another will walk along a beach and search for shells, shark teeth or other items the surf may wash up. One animal typically found is the starfish.

Actually, starfish are not fish at all. The major difference is that they don't have any bones and are called invertebrates, says Stephen T. Szedlmayer, Extension recreation fisheries specialist with the Alabama Cooperative Extension System.

Scientists prefer to call them sea stars to avoid confusion with fish or other vertebrates (having a backbone). Sea stars belong in the phylum Echinodermata, or spiny-skinned animals. They are a unique group of marine animals not closely related to any others.

The body form most familiar is the star shape, but this form can vary dramatically, from the very beautifully star-shaped and colored marginal sea star to the sluglike sea cucumber that may take a prize for one of the ugliest animals in existence, says Szedlmayer.

There are three main classes of Echinoderms -- sea cucumbers, sea urchins and sand dollars, and sea stars. Sea cucumbers can reach 12 inches in length. Sea cucumbers, such as the scarlet psolus, can be quite colorful. These are found in cold waters from Cape Cod to the Arctic. The common local species is olive, brown or black.

Almost everyone is familiar with sea urchins and sand dollars. Sand dollars are sold as jewelry or souvenirs in almost every beach resort. They are a flat disc-like animal about 4 inches across.

Sea urchins are another group in this class. They have many hard, sharp spines on a round shell. Sea urchins create a great deal of interest both biologically and economically. Biologically, an outbreak of sea urchins has caused substantial damage to coral reefs. Because sea urchins are easy to handle in the laboratory, many studies have been conducted in development biology using sea urchin eggs. You may have observed their various stages of development in a biology class.

Economically, harvesting of sea urchins for their eggs has started a new fishery. Harvesting of sea urchins has grown in the Pacific Northwest where harvested eggs are shipped to Japan.

Some sea urchins are dangerous to handle. In the Florida Keys, the long-spined Diadema antillarum, has hollow, needlelike spines that may contain poison. Injuries from their spines are extremely painful and spines can be difficult to remove.

The last class is sea stars and brittle stars. Sea stars are star-shaped, while the brittle stars have a center round disk with spiderlike arms. A bazaar biological aspect of sea stars is the fact that when certain species are cut in half, each half can grow into a complete new animal, Szedlmayer adds. It's interesting that brittle stars and sea stars can live in intertidal habitats or in the deepest, darkest, coldest parts of the ocean, where water pressure is tremendous.

Sea stars also cause economic problems by eating valuable mollusks, such as oysters and clams. Their feeding method is also one of the most unusual, says Szedlmayer.

"After a sea star wraps its arms tightly around an oyster, it applies slow steady pressure to open the victim with its hundreds of small tubed feet that act like tiny suction cups. After the oyster finally gives up and opens, the sea star ejects its stomach out of its body and surrounds the soft oyster body. Digestion then takes place, after which the sea star reabsorbs its stomach."

 When first observed, sea stars seem like docile small animals, but they can be voracious predators of oysters and clams. Watching lapse photography of sea stars clearly shows they are hunt and seek predators in marine waters.

SOURCE: STEPHEN T. SZEDLMAYER, Extension Recreation Fisheries Specialist, Alabama Cooperative Extension System, (334) 990-4858