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Description of Colpoda inflataColpodid ciliate, 35-90 microns, usually 40-60 x 30-50 microns. L-shape produced by marked preoral narrowing and hemispherical postoral portion which juts out at almost right angle. Oral apparatus in "corner" of angle. Horizontal portion of angle with small, shallow, but in silver preparations always recognizable (examined in 30 populations!) diagonal groove however, a postoral sack is absent. Keel straight to strongly convex, with 6-8 rounded notches which disappear in well-nourished individuals. Only slightly flattened, in dorsal and ventral view broadly wedge-shaped. Macronucleus mostly slightly ellipsoid, rarely globular, usually between oral apparatus and dorsal side, rarely in postoral or preoral portion; nucleoli globular to plate-like, also anastomosing and ramified. Micronucleus ellipsoid, flattened, attached to macronucleus. Contractile vacuole in median at posterior end, during diastole surrounded by small collecting vesicles; pulsation interval 15-20 seconds. Excretory pore almost in centre of posterior pole. Cytopyge slightly left of median, fecal balls spongy. Cortex rather firm, flexible. Extrusomes in several indistinct rows between somatic kineties, but elongate only slightly (to 2-5 microns). Populations without extrusomes may occur. Very likely they were overlooked, being very small (1.2 x 0.8-1.2 microns) and concealed in viscous ectoplasm. Cytoplasm colourless to yellowish, with fairly many 1-3 microns sized rod-shaped, yellowish crystals. Often packed tightly with 4-8 microns sized food vacuoles. Feeds almost exclusively on bacteria, rarely on flagellates. Swims clumsily, usually glides, soon resting for long periods on right side. This resting is, however rather a slow jerky circling on the spot, which is why the species is not as easy to photograph as the often perfectly immobile C. henneguyi. Somatic kineties only slightly spiralling, almost bow-shaped on right side. Those of right meet keel at steeper angle than those of left (similarly to C. ovinucleata). Second, sometimes also third somatic kinety interrupted at level of posterior half of vestibulum to produce 1-2 anterior kinety segments which consist of about 5 dikinetids each. 4-8 postoral kineties with fairly closely spaced dikinetids immediately left of vestibulum. A short diagonal groove is evidently present because these closely spaced dikinetids have the posteriorly inclined fibres which are characteristic for diagonal groove dikinetids. Minimum and maximum number of somatic kineties fairly variable (17-29), but usually average between 20 and 25. Vestibulum approximately equatorial in "corner" of angle relatively large. Vestibular opening is an inclined U-shape. Left polykinetid rhomboid to slightly spoon-shaped, very constant and unique to the species; with 13 kineties. Right polykinetid comprises about 7 kineties with rather regularly arranged basal bodies. No vestibular kineties.