Family: Unicells or cells loosely attached forming hyphae; cell body varied in shape, a constriction at the center in most species; cell walls consisting of two or more parts, with small pores and various ornaments (Illustrations of The Japanese Fresh-water Algae, 1977).
Genus: Cell body crescent in shape (long, curved, tapered at both ends); cross section rounded; cell wall smooth or with longitudinal lines, bands on the cell wall in some species; chloroplast laminae ridged and radially arranged, which makes cross section star-shaped; pyrenoids aligned or scattered (Illustrations of The Japanese Fresh-water Algae, 1977).
T=terminal; Tv=terminal vacuole

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Subgenus: Holopenium (Cell body straight; cell wall smooth)

C. libellula or C. closterioides 22 samples 100-244 μm L/W=4.2-6.4 1998-2008

C. libellula or C. closterioides 22 samples 100-244 μm L/W=4.2-6.4 1998-2008

C. navicula 8 samples 33-88 μm L/W=3.0-5.2 2003-2007

C. rectimarginatum ? 5 samples 106-218 μm L/W=6.3-11.0 1998-2008

Subgenus: Euclosterium (Cell body curved)

Cell wall smooth (or finely striated)
Cell body slightly curved
C. aciculare 13 samples 125-520 μm L/W=38-74 199?-2007	C. gracile 36 samples 64-320 μm L/W=17-44 1997-2008	C. macilentum 12 samples 255-600 x μm L/W=11-32 2004-2008	C. acutum v. acutum 2 samples 110-130 μm L/W=23-33 1998-2004
C. pronum 34 samples 99-590 μm L/W=33-50 1998-2007	C. idiosporum 24 samples 115-328 μm L/W=22-37 1998-2007	C. strigosum 6 samples 80-207 x 6-12 μm L/W=13-17 2004-2007	C. praelongum 23 samples 210-695 μm L/W=17-43 1997-2008
C. toxon 13 samples 107-324 μm L/W=15-22 1998-2008	C. cornu 11 samples 135-225 μm L/W=13-19 2000-2006	C. littorale 290 x 27 μm L/W=10.7 Yamaguchi Univ. Yamaguchi, 2004	C. sinense 130-50 x 14 μm L/W=9.3-10.7 Higashi-Urawa Saitama, 2001
C. lunula 22 samples 300-874 μm L/W=5.0-9.8 1998-2008	C. pseudolunula ? 260 x 50 μm L/W=5.2 Kami-takayanagi Kisai town Saitama, 2003	C. lanceolatum 6 samples 230-568 μm L/W=4.7-5.3 1999-2007	Closterium sp. C. lanceolatum ? 143 μm within gel sheath Narita Chiba, 2000
C. abruptum 36 samples 155-258 μm bands present 2003-2008	C. tumidum 100 x 17 μm L/W=5.9 ends truncated Kasuga Fukuoka, 2001	C. pusillum ? 30-46 x 7 μm L/W=4.3-6.6 Ikenokochi marsh Tsuruga Fukui, 2004	Closterium sp.9 295 μm L/W=18 Japan, 199?
Cell body strongly (or moderately) curved
C. ehrenbergii 30 samples 209-650 μm L/W=4.5-9.5 pyrenoids scattered 1999-2008	Closterium sp. C. ehrenbergii ? 1040, 980 x 96 μm Aquatic botanical g. Sawara Chiba, 2004	C. moniliferum 62 samples 155-380 μm L/W=4.7-9.0 199?-2008	C. moniliferum ? 230-255 x 50-55 μm L/W= Ichino-kawa Namegawa Saitama, 2004
C. leibleinii 13 samples 138-275 μm L/W=6.5-12.5 1998-2007	C. venus 8 samples 70-112 μm L/W=6.5-10 2003-2006	C. acutum v. variabile 8 samples 112 μm L/W=30-38 1998-2005	C. cynthia 27 samples 67-160 μm L/W=7.8-13.2 199?-2008
Small pores present at both termini
C. dianae 71 samples 100-460 μm L/W=7-16 1998-2007	C. dianae 71 samples 100-460 μm L/W=7-16 1998-2007	C. dianae 71 samples 100-460 μm L/W=7-16 1998-2007	C. calosporum 4 samples 108-156 μm 2003-2005
C. parvulum 6 samples v. angustum 120-140 μm 1998-2007	C. subulatum 3 samples 235-270 μm L/W=11-18 2004-2007
Cell wall dotted; cell body slightly curved
C. praelongum v. porosum 420 μm L/W=18 USA, 1999	C. baillyanum 25 samples 388-568 x 42-50 μm L/W=7.8-11.4 2004-2008
Cell wall striated
Cell body slightly curved
C. ulna 16 samples 112-396 x μm L/W=14-25 2003-2008	C. angustatum 9 samples 374-600 μm L/W=15.6-21.4 2003-2008	C. acerosum 89 samples 205-892 μm L/W=5-26 1998-2008	Closterium sp. 248 x 38 μm 335 x 34 μm L/W=6.5, 9.9 near City Hall Fujimi Saitama, 2004
C. turgidum 7 samples 562-785 μm L/W=13-17 1998-2008	C. lineatum 4 samples 292,3 x 21 μm L/W=21-25 1999-2007	C. intermedium 54 samples 214-500 μm L/W= 2001-2008	C. striolatum 24 samples ? 198-494 μm L/W=8.5-13.4 2000-2008
C. rostratum 47 samples 180-572 μm L/W=9.2-21 1999-2008	C. archerianum 2 samples strongly curved 280-324 μm L/W=11-13 2005-2006	C. archerianum ? 210 x 15 μm L/W=14.0 Kumakubo Nasu-shiobara Tochigi, 2005
C. ralfsii 37 samples center swelled pores at ends 215-600 μm 2001-2008	C. kuetzingii 34 samples 160-560 μm L/W=13-24 1999-2008	C. setaceum 18 samples 295-610 μm L/W=24-38 1998-2008
C. nematodes v. proboscideum 7 samples 262-400 μm 2004-2008	C. macilentum v. japonicum 12 samples 255-600 x μm L/W=11-32 2004-2008	C. wallichii ? x 44 μm Iyari marsh 3 Omachi Nagano, 2008
Cell body strongly (or moderately) curved
C. costatum 8 samples 190-660 x 27-63 μm L/W=8.9-11.5 Myoko highland 1999-2008