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Description of Colpoda steiniiColpodid ciliate,10-60 microns long, usually 20-40 x 15-30 microns. Body usually slightly reniform, dorsal (right) margin more or less distinctly convex, ventral (left) straight and slightly indented at oral apparatus, that is, somewhat above mid-body. Keel (ventral margin above oral apparatus) straight to slightly receding dorsally or projecting somewhat ventrally, with 5-7 notches. Starved specimens hyaline and strongly flattened (about 2:1), well-nourished cells dark and almost unflattened. Macronucleus slightly underneath mid-body, ellipsoidal, contains large nucleolus easily recognizable in live, slightly squeezed specimens. Contractile vacuole in posterior end. Extrusomes lie along ciliary rows (recognizable only after protargol impregnation). There are 10-13, usually 12, curved ciliary rows composed of basal body pairs; both basal bodies ciliated at least in anterior body third. Two caudal cilia about half as Iong as body, difficult to recognize in vivo because very motile. Third ciliary row right of oral apparatus slightly shortened posteriorly, ciliature distinctly reduced in left posterior area (details only recognizable with interference contrast optics or after silver impregnation, not necessary for identification. Oral apparatus in anterior third of cell, notches ventral side slightly to fairly distinctly. Left oral ciliary field invariably spoon-shaped (well recognizable in live, slightly squeezed specimens), consists of 8-12 short basal body rows with cilia extending beyond body proper, forming distinct "beard" . Swims and glides rather rapidly.