Genus: Generally ovoid; asymmetrical; plastic or rigid; a slit-like ventral furrow; flagella at anterior end; cytopharynx long; contractile vacuole anterior; nucleus posterior (Kudo, 1966). Lightly striated; trailing flagellum longer than anterior one (How to know the protozoa, 1979). Species: 25-40 μm long, 16-22 μm wide; rigid, oval; somewhat flattened; pellicle slightly striated (Kudo, 1966). Rigid; faintly spirally striated; fresh water (How to know the protozoa, 1979).

50 μm 100 μm 150 μm; x 400 : 31 μm 63 μm 94 μm; x 640

T. octocostatus Stein: 35-63 μm long; fresh water (Kudo, 1966). Ovoid, pointed at rear; notched at anterior; short flagellum 1/4 of longer one, both held anteriorly in locomotion; fresh water (How to know the protozoa, 1979).