rotifer (wheel animacule) Microscopic metazoan found mainly in freshwater. Although it resembles ciliate protozoan, it is many-celled with a general body structure similar to that of a simple worm. Rotifers may be elongated or round, and are identified by a crown of cilia around the mouth. Class Rotifera.

ro·ti·fer / ˈrōtəfər/ • n. any minute multicellular aquatic animal of the phylum Rotiferea, with wheellike ciliated organs used in swimming and feeding.