A sea star rests on a barnacle-covered rock.
A sea star rests on a barnacle-covered rock.
E. Zabel, courtesy of URI

Sea Star (Asterias forbesii)

Alternate common name: Forbes Sea Star, Starfish.
Color: Brownish purple to orange with lighter underside.
Size: Up to 12 inches across when mature.
Habitat: Rocky shores, tide pools, dock pilings, Bay bottom.
Seasonal appearance: All year.

Description

Sea stars are not fish as their nickname "starfish" suggests. They belong to a group of animals called echinoderms, which means "spiny skin." They are related to brittle stars, sea urchins, sea cucumbers, and sand dollars. Sea stars have five arms, or rays, connected to a small round body. Sea stars detect light with five purple eyespots at the end of each arm. The bright orange dot in the center of the body is called the madreporite. This organ pumps water into the sea star's body. This pumping action creates suction at the end of hundreds of tube feet, located in paired rows on the underside of the arms.

Life History and Behavior

Sea stars use suction in the tube feet for movement and feeding. They wrap their bodies around quahogs and other bivalves, using the suction from their tube feet to pull shells apart. When the prey is opened, the sea star pushes its stomach out of its body and into the bivalve, secreting enzymes that digest the prey's soft body tissues. The liquefied bivalve is then absorbed into the stomach. Sea stars feed often, and their size depends on the amount of food they eat, not on their age.

Sea stars are eaten by bottom-dwelling fish and crabs, as well as by sea gulls when low tides leave the sea stars exposed. Regeneration will occur as long as one fifth of the sea star's body remains intact. Sea stars breed in the spring, producing as many as 2,500,000 eggs. Females will feel plump and spongy when their arms are filled with eggs.

Special Notes


Adapted from The Uncommon Guide to Common Life on Narragansett Bay. Save The Bay, 1998.