Genus: Colonies of a fixed number of cells, flat, circular in shape; cell body polygonal in shape,
with horn-like projections; cell wall garanulated, wrinkled or notched;
chloroplasts plate-like or reticular; asexual reproduction by zoospore; sexual reproduction by isogametes
(Illustrations of The Japanese Fresh-water Algae, 1977).
Species: Colonies without perforations, 12-74 μm in diam.; all cells with a deep incision, cell wall smooth ; marginal cells with two triangular processes extending outward, triangular (colonies with small number of cells) or trapezoid (large colonies) at base, 5-18 μm in diam., 4-18 μm long; inner cells five to seven angled, 4-16 μm in diam., 4-14 μm long (Photomicrographs of the Freshwater Algae, vol. 5, 1986).