Species [var. praelongum]: Cell body 380-885 μm long, 11-26 μm, L/W = 22-24; slightly curved but straight at the center, tapered at both ends; curveture reversed at both ends, cell wall finely striated. [var. brevius Nordstedt ]: Cell body shorter than v. praelongum, 198-360 μm long, 13-24 μm, L/W = 10-22. [var. porosum (Gutwinski) Krieger ]: Cell body 120-557 μm long, 18-24 μm, L/W = 10-22; cellwall finely dotted, (Illustrations of the Japanese Fresh-Water Algae, 1977).

50 μm 100 μm 150 μm; x 400 : 31 μm 63 μm 94 μm; x 640