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

Difflugia mammillaris Penard, 1893
Syn.: Difflugia brychtai Stepanek, 1967

Diagnosis: Test ovoid, elongate, swollen or arched in the mid-region but tapering at both extremities, to give a rounded protuberance aborally and gradually near the aperture to give a slightly pronounced neck. Aperture circular, composed of small particles; in side view usually oblique. Aboral spine usually non-central. Nucleus spherical with central nucleolus. Nucleolus with some small lacunae.

Dimensions: Length 93-111 µm (Ogden), 90-130 µm (Penard) and 90-113 µm (Grospietsch). My measurements: 97-129 µm.

Ecology: Freshwater; different water types. Common species in sediments and detritus; when present, it is abundant.

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.

Difflugia mammillaris
Difflugia 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
Difflugia mammillaris
Difflugia mammillaris
Drawing: Penard, 1902 and shell with gas bubble for floating
Difflugia mammillaris
Shell 101 µm (l), Montfoort and Naardermeer (r), the Netherlands
Difflugia mammillaris
Difflugia mammillaris in division, each shell about 75 µm
Difflugia mammillaris
Difflugia mammillaris
Difflugia mammillaris – circular aperture
Difflugia mammillaris – note the strongly oblique aperture
Difflugia mammillaris
Difflugia mammillaris, 80 µm, Naardermeer
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