Centropyxis aerophila  Deflandre, 1929

Diagnosis: Shell small to medium size, usually circular in dorsal view, with strongly increased fundus and more flattened apertural region; aperture at the border of the shell, eccentric, largely elliptic or nearly circular; shell covered with closely-set sand grains and/or diatoms, giving a grey color to the test. Sides not or only slightly converging towards pseudostome having semi circular outline. Sides only slightly curved, often almost straight. In ventral view, abdomen seemingly separated from pseudostomal area, looking like being attached to the abdomen. Pseudostomal region more transparent than abdominal region in resin preparations.
Pseudostome usually semicircular with straight, occasionally slightly concave posterior margin. Abdomen distinctly inflated in lateral view, but steeply flattens towards pseudostome, whose anterior margin is more or less distinctly turned inside.
Test entirely chitinous, finely and irregularly punctuated or with rather distinct flakes, carries sometimes brown or dark organic debris and small quartz grains, colorless or yellowish. Occasionally rather dark brown yellow. At certain sites, shell often appears entirely covered with foreign particles. Pseudopodia and nucleus not yet observed.

Dimensions: overall size 53-85 x 42-66 µm; shell height about 2/3 of length; pseudostome 21-28 x 15-21 µm.

Ecology: mosses and Sphagnum.

Remarks: The varieties Centropyxis aerophila aerophila, C. aerophila sphagnicola and C. aerophila sylvatica, described by Deflandre in 1929 and later recorded by many workers worldwide, cannot be distinguished with the features provided in the original descriptions, and even not with refined morphometrical data, though C. aerophila sylvatica seems a distinct species. For practical purposes it is better to use the term C. aerophila-complex (Foissner and Korganova, 2000).