Entosiphon sulcatum: About 20 μm long (Kudo, 1966; How to know the protozoa, 1979); trailing flagellum more than twice the length of anterior one (How to know the protozoa, 1979); 20-25 μm long, 10-15 μm wide (Illustrated Guide, 1985); Cell body ovoidal with 6-7 longitudinal grooves, 20-30 μm long, 12-18 μm wide; anterior flagellum nearly the same as the cell body in length, trailing flagellum about twice of the cell body in length (An Illustrated Guide to Freshwater Zooplankton in Japan, 2000).