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:

31 μm 63 μm 94 μm; x 640

Images of collecting locality: Lake Biwa near Irie bridge, Maibara city (formerly Maihara town), Shiga Pref., Japan, June 30, 2008, by Y. Tsukii