Section [Margaritiferae]: Cell surface granulated, gnarled or spiny; semicells pyramidal with flattened apex or trapezoid (Illustrations of The Japanese Fresh-water Algae, 1977). Species [f. arcticum]: Cell body 35 μm long, 24 μm wide, isthmus 12.6 μm wide, both sides with 6 waves (including basal and apical corners), apex with 2 corners and 2 waves (Illustrations of The Japanese Fresh-water Algae, 1977).

31 μm 63 μm 94 μm; x 640