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Difflugia mammillaris
D. mammillaris, all shells from the same sample, 95-122 µm

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: Length 90-110 µm, up to 130 µm (Penard, 1902); 93-111 µm (Ogden), 90-113 µm (Grospietsch). 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 test 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.

Difflugia mammillaris
D. mammillaris, all shells from the same sample, 92-126 µm (Naardermeer, 2019)
Difflugia mammillaris
Difflugia mammillaris
Typical elongated S shape – Montfoort, the Netherlands
Difflugia mammillaris
Difflugia mammillaris
Nucleus, from populations in Naardermeer (L) and Gooimeer (R)
Difflugia mammillaris
Difflugia mammillaris
Drawing: Penard, 1902 and a shell from the Penard Collection (MHNG), specimen 285-1-2, labeled D. mammillaris.
Difflugia mammillaris
Shell 101 µm (l), Montfoort and Naardermeer (r), the Netherlands
Difflugia mammillaris
D. mammillaris in division, each shell about 75 µm
Difflugia mammillaris
D. mammillaris, 80 µm, Naardermeer
Difflugia mammillaris
D. mammillaris, Gooimeer, Netherlands, 2021
Difflugia mammillaris
D. mammillaris, Gooimeer. Note the square contour in top view.
Difflugia mammillaris
Difflugia mammillaris
D. mammillaris, Gooimeer. Square (L) and triangular (R) contour in top view.
Difflugia mammillaris
D. mammillaris, Gooimeer, Netherlands, with circular contour in top view.
Difflugia mammillaris
Difflugia mammillaris
D. mammillaris, Gooimeer, Netherlands, 2021
Difflugia mammillaris
Difflugia mammillaris
Shell with gas bubble for floating (L) and circular aperture (R)
Difflugia mammillaris
Difflugia mammillaris
Difflugia mammillaris
D.mammillaris, with circular aperture (L) and with strongly oblique aperture (R)
Ferry Siemensma, created February 23, 2019; last modified May 09, 2021
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