Source : Webster's Revised Unabridged Dictionary (1913)

Rotifer \Ro"ti*fer\ (?; 277), n. [NL. see {Rotifera}.]
   (Zo["o]l.)
   One of the Rotifera. See Illust. in Appendix.

Source : WordNet®

rotifer
     n : minute aquatic multicellular organisms having a ciliated
         wheel-like organ for feeding and locomotion; constituents
         of freshwater plankton