A class of the phylum Rotifera characterized by a single gonad and mixed sexual and asexual reproduction. Monogonont rotifers are a major invertebrate component of freshwater and coastal marine ecosystems as judged by biomass, ecological importance, and number of species. Some species of Brachionus are grown commercially at rates of more than 100,000 per day as food for aquaculture of larval marine finfish and crustaceans.