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 of 8, 16, 32 (sometimes 64, 128) cells, spherical or ellipsoid in shape, intercellular space absent; inner cells tetragonal to hexagonal, concaved at outer side; marginal cells with two long horn-like processes; a tuft of bristles projected from apex of the processes; zoospores produced within the mother cells; daughter colonies formed in a vesicle released from the mother cells; cell wall granulated (Photomicrographs of the fresh-water algae, 1993).