Genus (Ehrenberg): Cells usually fusiform; both ends hyaline; two euqal-length flagella, about 1/2 as long as cell; eye spot present in most species; two or several contractile vacuoles; trasverse division to form 4 zoospores; nutrition phototrophic or chemo-organotrophic (Illustrated Guide, 1985).
Species: Cell body fusiform or elogated ovoid, 17-59 μm long, tapered at both ends, cell wall thin, chloroplasts plate-like, with 2-8 pyrenoids, stigma ovoid or nearly spherical, located at anterior 1/6-1/4 of the cell body, many contractile vacuoles (An Illustrated Guide to Freshwater Zooplankton in Japan, 2000). Cell body 25-70(-100) μm long, 4-15(-20) μm wide (Ettl, Chlorophyta I, Süßwasserflora von Mitteleuropa Band 9, 1983). Cell body 60-80 μm long, 8-12 μm wide, 4-8 pyrenoids (Illustrations of The Japanese Fresh-water Algae, 1977).