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

 
Difflugia mammillaris Penard, 1893

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 grey.
This species resembles Difflugia elegans, but that species doesn’t have a rounded protuberance. It can also be confused with Difflugia varians.

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 – Montfoort, 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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