Family: Cell body cylindrical or spindle-shaped, loosely attached with each other to form a filamentous colony; cell wall smooth, consists of a single partition, one layer; 1-2 chloroplasts plate- or ribbon-like, with pyrenoids; a single nucleus centrally placed.
Genus: Cell body usuall large, spindle or cylindroid in shape, rounded at both ends; two chloroplasts star-shaped at cross-section, consisting of a central rod and radially arranged dented laminae (Illustrations of The Japanese Fresh-water Algae, 1977).

N. digitus 2 clips near Ayase river Fujimi Saitama, 1999	N. digitus 3 clips Numanobe Yamagata Yamagata, 1999
N. digitus 6 clips 282 x 56 μm L/W=5.0 Hiroshima, 1998	N. digitus 12 clips 263 x 63 μm L/W=4.2 Niigata, 2001