Rotifer (Platyias quadricornis)—Runk/Schoenberger—Grant Heilman

Any of about 2,000 species of microscopic, multicellular, water-dwelling invertebrates constituting the class Rotifera, or Rotaria (phylum Aschelminthes; see worm). Currents created by the rotifer's corona (moving cilia arranged in a circle at the head) sweep bacteria, protozoans, and detritus into the mouth. Rotifers also eat larger items (other rotifers, crustaceans, algae). The muscular pharynx contains hard jaws. Body shape varies greatly among species. Rotifers are common in freshwater on all continents, but some live in saltwater. The species vary widely in mode of living: they may be free-living or parasitic, solitary or colonial, and free-swimming, crawling, or sedentary.

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