Species: 250-(396-576)-790 μm long, 25-(33-84) μm wide; cell body large, slightly curved; both termini tapered; pyrenoids 7-15 in each semicell (Illustrations of The Japanese Fresh-water Algae, 1977). Cell body slightly curved, gradually attenuated toward the truncated ends, which somewhat recurved due to the covexity of the inner margin near the ends; inner margin straight or slightly concave, outer margin convex, 300-500 μm long, 32-50 μm wide, L/W=9-14; cell wall smooth and colorless or sometimes delicately striated and yellowish-brown in color; chloroplasts with ridges containing 7-11 pyrenoids in central row (Photomicrographs of the Freshwater Algae, vol. 1, 1984).
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Inner side slightly concaved; L/W=7-14 Cell body more than 40 μm in width
var. acerosum
40 samples
197-692 μm
L/W=7.5-14.2
1998-2007
var. acerosum
40 samples
197-692 μm
L/W=7.5-14.2
1998-2007
var. acerosum
40 samples
197-692 μm
L/W=7.5-14.2
1998-2007
var. acerosum
40 samples
197-692 μm
L/W=7.5-14.2
1998-2007Cell body 20-40 μm in width
var. acerosum
13 samples
206-560 μm
L/W=12-16
1999-2006
var. acerosum
13 samples
206-560 μm
L/W=12-16
1999-2006
var. acerosum
13 samples
206-560 μm
L/W=12-16
1999-2006
var. acerosum
13 samples
206-560 μm
L/W=12-16
1999-2006Cell body small (194-410 μm); L/W=7-11
var. minus ?
14 samples
194-484 μm
L/W=6-10
1998-2007
var. minus ?
14 samples
194-484 μm
L/W=6-10
1998-2007
var. minus ?
14 samples
194-484 μm
L/W=6-10
1998-2007
var. minus ?
14 samples
194-484 μm
L/W=6-10
1998-2007Cell body long (388-915 μm), central region nearly straight; L/W=15-33
var. elongatum
21 samples
303-892 μm
L/W=17-23
1998-2008
var. elongatum
21 samples
303-892 μm
L/W=17-23
1998-2008
var. elongatum
21 samples
303-892 μm
L/W=17-23
1998-2008
var. elongatum
21 samples
303-892 μm
L/W=17-23
1998-2008Inner side slightly convexed (336-494 μm); L/W=8-12
var. tumidum ?
312 x 19 μm
L/W=16
laminae irregular
Saitama, 1999