Treated as plural. A class or phylum of minute or microscopic aquatic animals comprising the rotifers and (formerly) certain ciliates; (also in form rotatoria) animals of this class or phylum (collectively or individually); rotifers, wheel-animalcules.
Mid 19th century; earliest use found in Edinburgh New Philosophical Journal. From scientific Latin Rotatoria from post-classical Latin rotatorius + -a, after earlier use as specific name (in scientific Latin Vorticella rotatoria (O. F. MuellerVerm I. i. 106)).