any of a class (Rotifera of the phylum Aschelminthes) of minute usually microscopic but many-celled chiefly freshwater aquatic invertebrates having the anterior end modified into a retractile disk bearing circles of strong cilia that often give the appearance of rapidly revolving wheels
any microscopic animal of the phylum (or class) Rotifera, found in fresh and salt waters, having one or more rings of cilia on the anterior end