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 ovoid to long triangular, slightly twisted; anterior broadly rounded, shallowly bilobed; laterally undulated and asymmetrical; posterior tapered into a long cauda; paramylon bodies (usually three) cup-shaped parietal plate; two located in the right and left anterior halves of the cell, one occupying the posterior half of the cell; cell body 22-26 μm long, 10-13 μm wide (Photomicrographs of the Freshwater Algae, 1995).

31 μm 63 μm 94 μm; x 640

Images of collecting locality: No. 4, Okahotto-Yatsu Museum (a biotope including rice field), Okahotto, Abiko city, Chiba Pref., Japan, February 17, 2008 by Y. Tsukii