Genus: Highly flattened; pellicle firm; body form constant (Kudo, 1966). Chloroplasts small, discoid, pyrenoids usually absent; most species flat and leaf-shaped; often with ridges or fins running helically or longitudinally (Illustrated Guide, 1985).
Species: Cell body 25-30 μm long, 24-26 μm wide, broad ovoid or nearly spherical at dorsal view; dorso-ventrally grooved; tail region short, not straight; two disc-shaped paramylons; a flagellum two-times longer than the body length (An illustrated guide to freshwater zooplankton in Japan, 2000).