Genus: Cell body short, with a deep constriction at the center, apical view fusiform or radially symmetrical; cell apexes without spiny projections; intermediate zone or folded structure appeared during cell division; zygospores remain within their mother cells (Illustrations of The Japanese Fresh-water Algae, 1977). Species: Cell body constricted in the middle, sinus narrow-linear part but acutely open outward, 11-22 μm long, 24-39 μm wide, L/W=2, constriction 21-28 μm wide; vertical view of cells triangular, sides straight, angles rounded; apex broad, with a short connecting process at each apical angle, excavated in the middle and forming a oblong hollow cavity between the adjacent cells; semicells transversely subrectangular, lateral margins obliquely truncate; filaments twisted (Photomicrographs of the Freshwater Algae, vol. 1, 1984).

31 μm 63 μm 94 μm; x 640

Images of collecting locality: Karakemi marsh, Yasaka, Omachi city (formerly Yasaka village), Nagano Pref., Japan, May 8, 2006 by Y. Tsukii