Section [ Calocylindrus ]: Cell body cylindrical, slightly constricted at the center,cell surface granulated or with knobs.
Species [ var. amoenum ]: Cell body cylindroid, 42-67 μm long, (22-28)-30 μm wide, L/W=2, isthmus 13-21 μm wide; cell wall covered with large granules, longitudinally arranging in 7-8 rows forming a cross (+) pattern on the cell wall; 2 pyrenoids in each semicell.
[ var. alternans ]: Cell body 44-45 μm long, 23-24 μm wide, isthmus 15.4 μm wide; granules arranging as an "X"-shaped pattern on the cell wall (Illustrations of The Japanese Fresh-water Algae, 1977).

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C. amoenum v. amoenum 43 x 20 μm Tashirodaira m.5 Hakkoda mountain Aomori, 2006	C. amoenum v. amoenum 46 x μm Omine numa Tsukiyono Gunma, 2003	C. amoenum v. amoenum 50 x 23 μm Omine numa Minakami Gunma, 2007.4	C. amoenum v. amoenum μm Omine numa 5 Minakami Gunma, 2007.10
C. amoenum v. amoenum 45-47 x 24-25 μm Shimo-no-koike Shiga highland Nagano, 2004	C. amoenum v. amoenum 49 x 25 μm Shimo-no-koike Shiga highland Nagano, 2006	C. amoenum v. amoenum ? 39 x 21 μm 44 x 24 μm Shimo-no-koike Shiga highland Nagano, 2004	C. amoenum v. amoenum ? 50 x 25 μm Shimo-no-koike Shiga highland Nagano, 2005
C. amoenum v. alternans ? 43 x 25 μm Shimo-no-koike Shiga highland Nagano, 2005	C. amoenum v. amoenum ? 45 x 24 μm Miyatoko m.5 Minami-Aizu Fukushima, 2008

Similar species -->> C. pseudoamoenum;

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