The free-living feather stars first appear in the Upper Triassic. They are related to starfish. As juveniles, they are attached to the sea bottom by a stalk, as their ancestors were. In the adult stage they break away from the stalk and can move about. Some can swim by undulating movements of the arms. Usually, feather stars creep about by using projections at the bottom of the crown, called cirri. They are the only crinoids in shallow water, and are all in the Order Comatulidae. Their flexible arms and ability to choose their feeding grounds was undoubtedly important in their success and survival.