Subgenus [ Eucosmarium ]: Cell body dorso-ventrally compressed, with strong constriction at the center, transverse section elliptical or diamond-shaped.
Section [ Microcosmarium ]: Cell surface smooth or dotted or punctated; semicells polygonal (Illustrations of The Japanese Fresh-water Algae, 1977).
Species: Cell body 15-(18-32)-34 μm long, 11.5-(12.6-22.4)-23 μm wide, L/W=1.5, constriction 2.8-8 μm wide, semicells half-ellipsoidal or rounded pyramidal, apices slightly depressed (cf. C. granatum ); cell wall with a small number of dots; a single chloroplast with a pyrenoid in each semicell (Illustrations of The Japanese Fresh-water Algae, 1977).

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Apex slightly depressed
C. laeve 21-23 x 14-16 μm Tokachi river Obihiro Hokkaido, 2005	C. laeve 24 x 19 μm Yamagata, 1999	C. laeve 21 x 17 μm near Railroad st. Truruoka Yamagata, 2005
C. laeve ? 19 x 16 μm History and folk m. Tajima Fukushima, 2004	C. laeve v. rotundatum μm O-ike park Yabuki Fukushima, 2003	C. laeve 26 x 19 μm Karasu river Takasaki Gunma, 2004
C. laeve 22 x 14 μm Karasu-ga-mori p. Nishi-nasuno Tochigi, 2004	C. laeve μm Sugata-gawa a.p. Shimotsuke Tochigi, 2008
C. laeve 23 x 19 μm Tsukuba Ibaraki, 2002	C. laeve var. rotundatum 22.5 x 16 μm Otto-Numa Ibaraki, 2002	C. laeve μm Koga museum Koga Ibaraki, 2003	C. laeve 25 x 17 μm near Yoshino park Mitsukaido Ibaraki, 2006
C. laeve μm Shiroyama Park Okegawa Saitama, 2002	C. laeve 21, 29 x μm Heisei-no-mori p. Kawajima Saitama, 2006	C. laeve 24 x 18 μm Kawashima or Kawajima Saitama, 2002	C. laeve 30 x 23 μm Ho-daisan-koen Yoshikawa Saitama, 2006
C. laeve 24 x 18 μm Takao-sakura p. Kitamoto Saitama, 2005	C. laeve ?? 22 x 21 μm Noda Namegawa Saitama, 2004	C. laeve ?? 22 x 20 μm Fureai-Hiroba Yoshimi Saitama, 2004
C. laeve or granatum ? 39 x 25 μm Nishi Urawa Saitama, 2001	C. laeve 21 x 16 μm Nishi Urawa Saitama, 2001	C. laeve 18 x 13 μm Kita-Urawa Park Saitama, 2002	C. laeve ? 34 x 25 μm Musashi-Urawa Saitama, 2002
C. laeve μm City Museum Iruma Saitama, 2003	C. laeve 21 x 16 μm City Museum Iruma Saitama, 2006	C. laeve 19 x 15 μm Iruma river Kawagoe Saitama, 2004
C. laeve v. octangularis ? 23 x 17 μm Iida-shinden Nishi-ku Saitama, 2004	C. laeve 24 x 17 μm Sannoh park Nishi-ku Saitama, 2004	C. laeve 20 x 15 μm Akanuma Hatoyama Saitama, 2004
C. laeve 28 x 19 μm 23 x 18 μm Kashiwa Chiba, 2002	C. laeve μm Hagoromo Park Chuo-ku Chiba, 2003	C. laeve ? 40 x 26 μm Hana-no-oka p. Inzai Chiba, 2006	C. laeve 22 x 15 μm Todoroki g.l. Kawasaki Kanawaga, 2004
C. laeve v. reniforme ? 25 x 18 μm Numa-no-hara m. Madarao highland Niigata, 2005	C. laeve 18 x 12 μm Inari Park Toyama, 2002
C. laeve v. rotundatum μm Shiroyama park Nagano Nagano, 2003	C. laeve 18 x 13 μm Kamisuwa r.w.st. Suwa Nagano, 2005	C. laeve v. octangularis ? 22 x 15 μm near Karakemi m. Omachi Nagano, 2005
C. laeve μm Kanazawa Univ. Ishikawa, 2003	C. laeve ? 22.5 x 18 μm Matto Ishikawa, 2002	C. laeve μm Kaga-city C.P. Kaga Ishikawa, 2007
C. laeve 20 x 14 μm near Railway st. Tsuruga Fukui, 2004	C. laeve 26 x 19 μm Kitayama park Nishi-no-miya Hyogo, 2004	C. laeve ? 28 x 19 μm Takamatsu Kagawa, 2002

Similar species -- >> C. scopulorum; C. granatum;

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