|Description of Frontonia atra: Peniculine ciliate, 100-400 micrometres in length, easily confused with the smaller Frontonia acuminata (60-150 micrometres). Body as a flattened lemon, rounded anteriorly, tapering in the posterior to a blunted point. Darkly pigmented cytoplasm, sometimes with a colorless zone at each pole of the cell, or with a darkly pigmented spot in the anterior third. Cytostome a rounded triangle, with the wide end toward the posterior; long postoral and short preoral suture. Single macronucleus, ellipsoid; single contractile vacuole, nearly equatorial on right side. Abundant trichocysts. Common and widespread in fresh water. Feeds on diatoms and other algae.