Brittle Star

  Brittle stars usually have five long, thin, jointed arms covered with spines; sometimes they have six or seven arms. Brittle stars can be as large as 2 ft (0.6 m) in diameter or as small as a few millimeters.  The arms of brittle stars are attached to a central disklike body that houses on the underside the mouth and jaws, stomach, and saclike body cavities called bursae, which are peculiar to ophioroids. The mouth is surrounded by five moveable jaw segments, making the mouth opening look like a star.  The larva, which develops from a fertilized egg, is called an ophiopluteus and is free swimming in the plankton until it transforms into the juvenile stage when it settles on the bottom of the ocean. Brittle stars are either male or female, although a few individuals are hermaphrodites. Brittle stars spawn at the end of summer, and most species release their eggs into the plankton and invest no parental care thereafter. They can also reproduce asexually; if an arm breaks off and it still has a small piece of the central disk attached, the arm can regenerate into a whole new brittle star.  Each arm is supported by a central internal skeletal support (ossicle). Like starfish, brittle stars have tube feet, but those of brittle stars lack suckers. The tube feet help more with feeding than with locomotion. Like other echinoderms, brittle stars can regenerate lost parts. If an arm is broken off, a new one grows in its place within months. If an arm is injured, the star can cast off the injured arm (autotomy) and then eventually grow a new one.  Brittle stars are also known as serpent stars.