Cyclopyxis eurystoma Deflandre, 1929

Diagnosis: Shell yellow to brown, circular in frontal view and hemispherical in lateral view. Shell surface rough except for the apertural collar. Aperture circular, central, relatively large, bordered by a smooth band of organic cement, slightly but distinctly invaginated.

Dimensions: Deflandre (1929): diameter 60—66 µm; height 49—52 µm; aperture 32—34 µm.
Todorov and Bankov (2019): diameter 50—78 µm; height 33—56 µm; aperture 21—40 µm.
Other workers: diameter 69—80 µm; height 46—55 µm; aperture 34—46 µm.

Ecology: Mosses, Sphagnum

Remarks: >This species may be confused with Phryganella acropodia, but the aperture of C. eurystoma is generally larger relative to shell diameter and is distinctly invaginated, whereas the aperture of P. acropodia is not.

Varieties and forma:
C. eurystoma f. alta Jung, 1942
Differs from the typical form by a higher shell. Shell diameter 37–40 µm; shell height 45–47 µm; aperture diameter 13–16 µm.

C. eurystoma sinuosa Decloitre, 1970
Differs from the typical form by a concave aperture. Shell diameter 35 µm; shell height 40–45 µm; aperture diameter 20 µm.