Difflugia mammillaris Penard, 1893
Syn.: Difflugia brychtai Stepanek, 1967
? Syn.: Pentagonia shablensis Todorov & Golemansky, 1998

Diagnosis: Shell ovoid-elongated, swollen, sometimes vaguely pyriform, almost always a little uneven in its contours, and terminated behind by a more or less well defined nipple. The cross section gives a figure roughly oval or elliptical, but irregular. The longitudinal contours are arched, and end in a rounded aperture, with a lip roughly serrated by the protrusion of the scales. Shell colorless, formed of a hyaline chitinoid substance embedded with amorphous, thin, irregular, small scales. Nucleolus with some small lacunae.

Dimensions: According to Penard (1902): Shell length 90-110 µm, up to 130 µm. Ogden: 93-111 µm, Grospietsch: 90-113 µm. My measurements: 75-126 µm. In the original description Penard mentions a length of 90-300 (!) µm, but obviously corrected it in 1902.

Ecology: Freshwater; different water types. In sediments and detritus.

Remarks: The shell and its extremity can strongly vary, but nevertheless this is a distinct species, easy to recognize when several shells within a population can be observed. Though Ogden describes the test as colorless, my specimens were always light brown or dark gray.
This species resembles Difflugia elegans, but that species doesn’t have a rounded protuberance. It can also be confused with Difflugia varians. It was also described by Stepanek (1967) as D. brychtai, and by Todorov & Golemansky (1998) as Pentagonia shablensis.