Species [var. setaceum]: 
Cell body quickly attenuated toward both ends (cf. C. ralfsii), 
each extended part longer than spindle-shaped part at middle (cf. C. kuetzingii), 
150-(252-528)-600 μm long, 6-(8.6-17) μm wide, 
L/W=30-33; cell wall transparent or slightly yellowish, finely striated 
(Illustrations of The Japanese Fresh-water Algae, 1977). 
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Images of collecting locality: 
Wetland II, Kashibaru marsh, Karatsu city, Saga Pref., Japan, September 9,  2008 by Y. Tsukii