Species: Cell body quickly attenuated toward both ends (cf. C. ralfsii), each extended part shorter than spindle-shaped part at middle (cf. C. setaceum), both termini slighlty curved, rounded, 270-690 μm long, 14-27 μm wide ( L/W= 18-20); cell wall transparent or brownish with thin lines (8-10 lines/10 μm wide); chloroplasts composed of 5 lamellae; 4-6 pyrenoids in each half-cell (Illustrations of The Japanese Fresh-water Algae, 1977). 270-512 μm long, 13-22 μm wide ( L/W= 18-30); 8-11 lines/10 μm wide (Photomicrographs of the Fresh-water Algae, vol. 4, 1985).

Similar species -->> C. ralfsii; C. setaceum;

31 μm 63 μm 94 μm; x 640

Closterium kuetzingii Brébisson, cell body 550 μm long, 20 μm wide, L/W=27.5, cell wall striated, x 200, x 400, x 640, Onnenai, Kushiro marsh, Kushiro city, Hokkaido, Japan, October 16, 2005 by Y. Tsukii

Closterium setaceum Ehrenberg var. setaceum f. setaceum: Cell body small in size, elongate, L/W= 30-42, 252-528 μm long, 6-16 μm wide; both termini slightly curved, spindle-shaped at middle; cell wall transparent or brownish with thin lines (8-13 lines/10 μm wide); 2-3 pyrenoids in each half-cell (Photomicrographs of the Fresh-water Algae, vol. 6, 1997).

* Closterium kuetzingii BrébissonBrébisson var. kuetzingii: Cell body moderate in size, elongate, L/W= 18-30, 270-512 μm long, 13-22 μm wide; both termini slightly curved, spindle-shaped at middle; cell wall transparent or brownish with thin lines (8-11 lines/10 μm wide); chloroplasts composed of 5 lamellae; 4-6 pyrenoids in each half-cell (Photomicrographs of the Fresh-water Algae, vol. 4, 1985).