Species [var. senarium ]: Cell body 21-31 μm long (excluding spiny projections), 29-36 μm long (including spiny projections), 27-34 μm wide (including spiny projections), isthmus 8.4-12 μm wide. [ var. simplex Hirano ]: Smaller than var. senarium, 23 μm (excluding spiny projections), 44 μm (including spiny projections), 43 μm wide (including spiny projections), isthmus 7 μm wide; projections at posterior side margins of semicells are simple spines (not dichotomous). [ var. nigrae-silvae Schmidle ]: 2 ring of dented structures surrounding each corner, 29 μm (including spiny projections), 36.4 μm wide, isthmus 12.5 μm wide (Illustrations of The Japanese Fresh-water Algae, 1977)

31 μm 63 μm 94 μm; x 640

Images of collecting locality: No.2, Kuroyachi marsh, Hachimantai, Hachimantai city, Iwate Pref., Japan, August 23, 2007 by Y. Tsukii