Description of Colpoda aspera:
Colpodid ciliate, 12-42 microns long. Shape less reniform than in other colpodids usually more semicircular, left margin almost straight due to very shallow indentation at oral apparatus. Right margin (dorsal side) moderately to strongly convex, appears slightly rugged due to lobe-like processes of pellicle. Anterior end sharply tapered to bluntly pointed, posterior broadly rounded. Keel with 4-5 distinct notches, straight to slightly receding. Inconspicuously flattened, broadly wedge-shaped. in ventral and dorsal view, no postoral sack. Macronucleus globular to slightly ellipsoid about 8 microns, usually somewhat below mid-body right of median. Nucleolus composed of many 0.4-0.8 microns sized granules, usually arranged in broad bands along periphery, often resulting in cross-shaped pattern. Micronucleus comma-shaped, attached to macronucleus, about 4 x 1.3 microns. Contractile vacuole and excretory pore at posterior end slightly right of median. Extrusomes tiny (< 1 microns), globular, colourless, along somatic kineties in pellicular ridges do not stain with protargol. Cortex thin, soft, with lobe-like to tooth-like processes along somatic kineties, projecting about 0.3 microns preorally and up to 1 microns postorally. These minute processes are difficult to recognize, especially in well-nourished specimens, demanding much patience and good optical equipment (interference contrast). Cytoplasm with few to many (20-40) rod-shaped darkly contoured crystals concentrated around contractile vacuole. Feeds on bacteria and fungal spores. Food vacuoles small, about 2-5 microns, not very compact. Movement moderately rapid, without peculiarities. Cilia about 6 microns long, in posterior half of cell usually only the posterior basal body of each pair is ciliated. There is, however, some variability in this respect. In most populations 12, rarely 14-16 somatic kineties (2 to 3 postoral). Kinety 2 has 3-5 closely spaced dikinetids below vestibular opening. Vestibulum small, slightly pre-equatorial, covers proximal half of left polykinetid. Left polykinetid slightly sigmoid; with small notch at distal end. The notch is due to the distal 3-4 kineties having only 2-3 basal bodies, whereas the following possess 4; occasionally 5. Cilia approximately 5 microns long, projecting left body margin. Right polykinetid inconspicuous, very similar to that of other small species, forms an angle of 60-70 degrees with left polykinetid.