(Müller, 1773)
Ehrenberg, 1830
Outline slightly triangular, right margin convex, left almost straight, broadly rounded anteriorly, transversely truncate posteriorly, with more or less distinct projection in oral area. Dorsoventrally flattened. Dorsal surface convex, smooth, occasionally with several indistinct longitudinal ribs. Pellicle stiff. Macronucleus horseshoe-shaped, 1 micronucleus. Contractile vacuole at level of transverse cirri. Seven ventral, 5 transverse cirri. Dorsal kineties 5-6 in number, no caudal cirri. Oral apparatus bipartite: 3-4 tiny frontal membranelles in deep indentation on anterior left, slightly covered by anteriormost frontal cirrus; 10-15 adoral membranelles in oval oral cavity on posterior left. Six longitudinal dorsal silverlines, rightmost connects basal bodies arc-like, second from right shortened and only in posterior body half; ventral silverline system wide-meshed. Size 35-50 x 30-45 µm.
Ref.: Wu and Curds (1979), Song and Wilbert (1989), Foissner et al. (1991).