Brittle Star, a marine animal related to the starfish, sea cucumber, sea urchin, and sand dollar. These animals are echinoderms—they are spiny-skinned and usually have a five-part body plan with radial symmetry. There are more than 1,800 species of brittle stars worldwide. They live in crevices in coral reefs or in the hollow insides of tube sponges and vase sponges.The brittle star has five slender, flexible arms
The brittle star has five slender, flexible arms extending from a central disk; the mouth, shaped like a five-pointed star, is on the underside of the disk. Depending on the species, the arms are 1 to 10 inches (25 mm to 25 cm) long; the disk is ¼ to 1 ¾ inches (6 to 44 mm) in diameter. The arms are used for grasping food and for locomotion. On the underside of each arm are two rows of tube feet (tiny muscular projections), which serve as sense organs. Unlike most animals, a brittle star can regenerate an arm that is broken off, as in a fight with a predator. To frighten off predators, some brittle stars become luminescent, producing flashes of green light.
The arms of a brittle star do break easily. But that doesn’t bother this echinoderm. Like a sea star, a brittle star can replace a missing arm. A brittle star sometimes even makes its arms come off when an enemy attacks it. That way, the enemy gets just a bite of the brittle star—but not all of it.
Brittle stars have five arms each and a lot of tube feet, just as many sea stars do. Brittle stars look similar to sea stars, but there are differences. Brittle stars do not have suckers on their tube feet. And their arms are usually longer and thinner than those of sea stars.
With its long, thin arms, a brittle star can move about quite easily. This echinoderm uses its arms as oars as it glides across the ocean floor. A brittle star is sometimes called a serpent star because of the way it “snakes” about in the water.
A basket star is closely related to a brittle star. But each of a basket star’s arms has branches—much like the branches of a tree. When a basket star stretches out its arms, it can use them like a basket. Plankton drifting by get caught in the basket and become food for the basket star.
Some kinds of basket stars remain hidden during the day. At night, they come out and stretch their arms to catch a meal. After “sifting” the water for food, the basket stars collapse their arms and find places to rest. Once in safe spots, they eat their catches by scraping their arms across their teeth.
Brittle stars are in the class Ophiuroidea of the phylum Echinodermata.