Facts: The Brittle Star

Brittle stars are echinoderms that are closely related to starfish. They typically have five very flexible arms that they use for locomotion. They can move quite rapidly by wriggling their arms. The arms are joined at a central disc that contains their vital internal organs. The arms are typically covered in delicate spines. Their spines may be so dense that they give their arms a fuzzy appearance. Brittle stars can voluntarily detach their arms if attacked by a predator. The missing arms can regenerate. Their mouth is located on the underside of their disc. Their body is supported by an internal skeleton of calcium carbonate plates. There are over 2000 different species of brittle stars. The largest have arms that can reach 24 inches long. They inhabit all oceans in both deep and shallow waters. The majority of species are bottom dwellers. Brittle stars may hide under rocks, in crevices, or on other organisms like coral and sponges. They may also bury themselves in sediment. They are common in tide pools and reef flats. Feeding tactics vary by species. Some feed by extending their arms to snatch nutritious particles out of the water column. Their tube feet help gather the food particles and transfer them to their mouth. Some are scavengers and some are predators that prey on small animals like crustaceans and mollusk. Any undigested material that they eat must pass back out of their mouth. Brittle stars are sensitive to light and will typically scurry for cover when exposed. Research on some species has shown that their body is covered with tiny transparent calcite crystals that act to focus light onto their light-sensitive tissues underneath. This forms an array that functions as a single eye. They have chromatophores that can be used to change color by expanding and contracting. They usually become lighter in color at night. The nerve endings in their skin can sense chemicals in the water and touch. They usually become sexually mature at about 2 years old. Many species are broadcast spawners that release their eggs into the water. Others may brood their eggs. Some species can reproduce asexually by fission. They accomplish this by splitting their disc in two and regenerating the half that was split. They generally live up to 5 years. Some brittle stars have been observed exhibiting bioluminescence. They may use this ability to glow to deter predators. For more marine facts, click the SUBSCRIBE button!!