Genus: Free-swimming; rigid oval; ventral surface convex; dorsal surface with a longitudinal groove;
flagella anterior; one long, directed anteriorly; the other shorter and trailing; fresh water
Species: Posterior end truncate or concave; about 22 μm long (Kudo, 1966). Wide lateral groove; second flagellum short, in groove, hard to see; resembles Petalomonas (How to know the protozoa, 1979).
N. apocamptus Stokes: Much compressed; dorsoventrally flattened; ventral face concave; 6-10 μm long, 5-6 μm wide, 3-4 μm thick; long flagellum straight during swimming, with minute waves at the tip (Illustrated Guide, 1985).