Species [ var. depressum ]: Cell body small in size, wider than length, 33-50 μm long, (36.5-47.5)-50 μm wide, isthmus 10-15 μm wide; semicells depressed ellipsoid, with slightly flattened apex, side view circular, apical view elliptical, with a single pyrenoid.
[ var. minor W. et G.S. West ]: Cell body smaller than var. depressum, 21-28 μm long, 21-25.3 μm wide, isthmus 4.3-8.4 μm wide; semicells elliptical diamond-shaped.
[ var. achondrum (Boldt) W. et G.S. West ]: Cell body 36-51 μm long, 40-52 μm wide, L/W=1.0; isthmus 11-17 μm wide; semicells hexagonal ellipsoid, apex broad, flattened (Illustrations of The Japanese Fresh-water Algae, 1977).

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var. depressum: Semicells depressed ellipsoid, 33-50 μm long, 36-50 μm wide
C. depressum v. depressum 30 x 30 μm Uruguay, 1999	C. depressum or C. contractum ? 38 x 30 μm Aka-ike Madarao highland Niigata, 2006
var. minor: Semicells elliptical diamond-shaped, 21-28 μm long, 21-25 μm wide
C. depressum v. minor ? 26 x 24 μm Kenashitai Hakkoda mountain Aomori, 2005	C. depressum v. minor ? 24 x 21 μm Imou bog Toyohashi Aichi, 2005	C. depressum v. minor ? 28 x 24 μm Imou bog Toyohashi Aichi, 2006	C. depressum v. minor ? 28 x 25 μm 23.5 x 21 μm near Uba-ga-daira Nasu Tochigi, 2006
var. planctonicum: Semicells reniform, 25-26 μm long, 25-26 μm wide
C. depressum v. planctonicum ? 23 x 22 μm Iroha-numa Zao mountain Yamagata, 2005	C. depressum v. planctonicum 22 x 19 μm Iroha-numa 2 Zao mountain Yamagata, 2006	C. depressum v. planctonicum ? 26.5 x 23 μm Kashibaru marsh 5 Karatsu Saga, 2006	C. depressum v. planctonicum ? 28 x 25 μm Shibu-ike Shiga highland Nagano, 2005
f. minuta: Semicells elongated ellipsoidal, 22.5 μm long, 28 μm wide
C. depressum f. minuta 22 x 25 μm Karakemi marsh Omachi Nagano, 2006	C. depressum f. minuta 24 x 25 μm Ohnuma Nasu-shiobara Tochigi, 2007	C. depressum f. minuta μm Kannon-numa 10 Nasu-shiobara Shimogo, 2008	C. depressum f. minuta μm Kannon-numa 11 Nasu-shiobara Shimogo, 2008

Similar species -- >> C. bioculatum; C. contractum;

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