feather star, common name of a class of echinoderms that, as juveniles, are attached to the sea bottom by a stalk with rootlike branches; the mouth side faces upward. In the adult stage they break away from the stalk and move about freely. Feather stars have water-vascular (ambulacral) systems, similar to those in other echinoderms, that extend into the branched arms on the body, or crown. Some can swim by undulating movements of the arms. Feather stars creep about by means of projections at the base of the crown, called cirri, which can grasp bottom objects. They are marine animals, like all echinoderms, and are widely distributed. They are most common in relatively shallow, warm waters, but some live in cold water and a number of species occur in the ocean depths. Like other members of this class, feather stars may form extremely abundant local aggregations. Feather stars are classified in the phylum Echinodermata, class Crinoidea.