Genus: Elongate, with a broad rounded or truncate posterior end during locomotion; highly plastic; delicate pellicle shows a fine striation; a free flagellum, long and conspicuous, tapers toward free end; a second flagellum adheres to the pellicle; a contractile vacuole, anterior, close to the reservoir (Kudo, 1966).
Species: 40-70 μm long (Kudo, 1966); 20-80 μm long (Illustrated Guide, 1985); 20-70 μm long (How to know the protozoa, 1979). 22-70 μm long, 10-20 μm wide (Illustrations of The Japanese Fresh-water Algae, 1977).