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Difflugia bicornis
D. bicornis, after Penard, 1890

Difflugia bicornis Penard, 1890

Diagnosis: Test transparent, ovoid or spherical, slightly compressed. Usually with two, but sometimes with one spike located aboral. Contour uneven, test covered with small and medium grains of sand, diatoms, flagellate cysts. The spike is covered with fine grains of sand. The aperture is round.

Dimensions: Penard (1890): Length 85-105 µm. My measurements: Length 115-143 µm (n=13; ten tests with two horns and three with one). L/W ratio 1.4-1.6.

Ecology: Freshwater, first described from Wiesbaden, Germany.

Remarks: Penard’s measurements correspond well with those of D. elegans. It might be possible that his D. bicornis is identical with that species. However, when I had a culture of D. elegans, I have never observed specimens with two horns.

Difflugia bicornis
D. bicornis, both tests from the same location, between a population of D. elegans and D. elegans var. angustata. These tests were 115-143 µm, where the D. elegans shells were smaller, 69-104  µm (see below).
Difflugia bicornis
D. bicornis, plot of a number of measurements of shells from the Gaasterland location, July 2019. It might be possible that D. bicornis falls within the variation of D. elegans, but those shells are much smaller.
Difflugia bicornis
Difflugia bicornis
D. bicornis, nucleus 24 µm, Gaasterland, 2019
Difflugia bicornis
Difflugia bicornis
D. bicornis, from Gaasterland, 2019
Difflugia bicornis
D. bicornis, from the Pénard Collection, Geneva – Photograph by Thierry Arnet, as part of the Pénard project.
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