Species [ var. circulare ]: Cell body large, nearly circular or slightly broad elliptical in shape, (51-75)-95 μm long, 48-90 μm wide, isthmus 20-(22-28)-34 &3956;m wide; semicells semicircular, basal corner rounded, side view ovoid or nearly circular, apical view elongated elliptical; cell wall covered with small dots; chloroplasts with 2 pyrenoids. [ f. minor ]: Cell body 33-35-(40) μm long, 35-(47) μm wide, isthmus 12-14-(17) μm wide (Illustrations of The Japanese Fresh-water Algae, 1977).

50 μm 100 μm 150 μm; x 400 : 31 μm 63 μm 94 μm; x 640