Species [ var. connatum ]: Cell body 22-24 μm long, 19.6-25 μm wide (excluding spines), isthmus 7-9 μm wide; spines short; semicells inverted semicircle in shape, apex flat or slightly convex. [ var. pseudamericanum Grönblad ]: Cell body larger than v. connatum 39-45 μm long, 25-36.45 μm wide (excluding spines), isthmus 5.6-11 μm wide; corners of semicells protruded upward making its apex concave. [ var. rectangulum Roy et Bisset ]: Cell body 14-20 μm long, 14.7-20 μm wide (without spines), isthmus 3.5-5.6 μm wide; side margins of semicells not convex; spines longer and thicker than v. connatum (Illustrations of The Japanese Fresh-water Algae, 1977)

31 μm 63 μm 94 μm; x 640

Images of collecting locality: No.1, a small pond (Sumano-simo-tameike) near Prefectural road route 272 (Tsukiyono-Sarugakyo-Onsen-sen), Tsukiyono, Minakami town, Gunma Pref., Japan, October 12, 2008 by Y. Tsukii