the larva of echinoderms of the class Ophiuroidea. An ophiopluteus has four pairs of long processes, or arms, enclosing calcareous rods. These arms, which are covered with a strip of ciliate epithelium, enable the larva to swim. Three pairs of coelomic sacs extend from the intestine; the left anterior sac opens to the outside through an interstitial canal. The adult form develops from the anterior part of the larva only.