Species [ var. minutum ]:
Cell body cylindrical, 50-230 μm long, 7-18 μm wide, L/W=8-12;
semicells not swelled at base, slightly tapered, with blunt and smooth ends; cell wall smooth or finely dotted;
chloroplasts located along cenral axis, with about 6 laminae; pyrenoids arranged linearly, 3-7 in each semicells.
[ var. elongatum (W. et G.S. West) Cedergren ]:
257-550 μm long, 8-16 μm wide, L/W=28-40;
[ var. crassum (W. West) Krieger ]:
Shorter and wider than v. minutum, 40-102 μm long, 12-20 μm wide, L/W=4-5;
[ var. cylindricum (Borge) Krieger ]:
175-300 μm long, 15.5-21 μm wide, L/W=14-15;
[ var. gracile (Wille) Krieger ]:
Thinner and longer than v. minutum, 110-240 μm long, 6.5-15 μm wide, L/W=14-20;
[ var. latum Kaiser ]:
Wider than v. minutum, 160-352 μm long, 19-28 μm wide, L/W=8-11
(Illustrations of The Japanese Fresh-water Algae, 1977).
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