Genus: Body more or less ovo-cylindrical; rigid with spirally striated pellicle; often with a short posterior spinous projection; stigma sometimes present; discoidal chromatophores (chloroplasts) numerous and marginal; paramylum bodies usually large and ring-shaped, laterally disposed; without pyrenoids; fresh water (Kudo, 1966).
Species: Cell body ovoidal, both ends rounded, 30-45 μm long, 22-31 μm wide; anterior end slightly depressed, whereby an opening for a canal located (near but not at the center of the apical end); locomotive flagellum long (about twice of the body length); a single paramylon body disc-shaped; pellicle spirally-striated at right hand; stigma large (An Illustrated Guide to Freshwater Zooplankton in Japan, 2000).