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.