Subgenus: Eucosmarium
Genus: Unicellular; variable in shape; a constriction at the center of the cell body; mostly longer than wide; flattened; each semicell hemispherical, spherical, ellipsoidal, rectangular, pyramidal or kidney-shaped; no apical indentation.
Subgenus: Cell body dorso-ventrally compressed, with strong constriction at the center, transverse section elliptical or diamond-shaped (Illustrations of The Japanese Fresh-water Algae, 1977).
Section Pyramidatae: Cell surface smooth or dotted or punctated; semicells pyramidal with flattened apex or trapezoid All margins smooth (not wavy)
C. granatum
16 samples
25-41 μm
1998-2007
C. pyramidatum
8 samples
77-84 μm
1999-2007
C. pseudopyramidatum
12 samples
49-71 μm
2003-2008
Cosmarium sp.
41 x 29 μm
Kami-hashi
Namegawa
Saitama, 2003
Cosmarium sp.
32 x 21 μm
Kurome river
Asaka
Saitama, 2004
C. subtumidum
27 samples
19-49 μm
1998-2008
C. succisum
5 samples
10-14 μm
2001-2004
C. trilobulatum
1 sample
35 x 23 μm
Omine numa
Gunma, 2003
C. dorsitruncatum
μm
Ohdo-ike
Chuo-ku
Chiba, 2007
C. dorsitruncatum ?
46 x 50 μm
Kejo-numa
Furukawa
Miyagi, 2003
C. dorsitruncatum ?
33 x 30 μm
Kejo-numa 1
Osaki (=Furukawa)
Miyagi, 2006
C. dorsitruncatum ?
μm
near Omine mt.
Minakami
Gunma, 2007
C. synduorhabdum ?
30 x 26 μm
Uruguay, 1999
C. hammeri
v. protuberans
7 samples
μm
1998-2008
C. incertum ?
μm
Ohyachi 2
Hachimantai
Akita, 2007Margins wavy
C. visbyense
2 samples
32-45 μm
single pyrenoid
1998-2004
C. notabile ?
Margaritiferae ?
5 samples
21-42 μm
1997-2004
Movies
C. suborthogonum ?
23 x 21 μm
Yasuji-kawa
Sawara
Chiba, 2004