Euglypha rotunda Wailes and Penard, 1911

Diagnosis: Shell ovoid, more or less compressed, varying in transverse section from circular to oval as it tapers from the mid-body region to the aboral region; shell composed of approximately one hundred and twenty, oval, shell-plates; aperture circular and surrounded by eight to fourteen evenly spaced apertural-plates; each apertural-plate is ovoid, thickened at the denticulate margin and carries a large median tooth which is bordered by two or three smaller teeth; nucleus with one central nucleolus; two contractile vacuoles. All parameters show a rather great variability, especially the size of the idiosomes and the diameter of the aperture.

Dimensions: Shell length 22—60 µm, width 11—26 µm, aperture diameter 6—12 µm, scale size is 2.5—8.0 µm.

Habitat: Sphagnum and other mosses, also in sediments.

Remarks: This ‘species’ Euglypha rotunda was shown to be an assemblage of small species whose morphology had been overlooked. Differences between these forms resided mainly in the shape of the aperture scales (Wylezich et al. 2002), as predicted by Coûteaux (1978).
In both cultured and wild animals variation appears to be restricted to the occasional large individual, usually having double the normal complement of shell and apertural-plates. (Hedley & Ogden, 1973).

Infraspecific taxa.
E. rotunda dorsalis Decloitre, 1969
The shell is bilaterally symmetrical, the ventral side is flattened, the dorsal side is slightly curved. The cross section is elliptical. The coating is made up of translucent, colorless oval idiosomes. The aperture is oval, located at an angle to the longitudinal axis of the shell. The shell length is 33—38 µm, the shell width is 17—24 µm, the shell thickness is 15—17 µm, the aperture diameter is 5—8 µm.

E. rotunda obliqua Decloitre, 1956
Differs from the typical form by its curved shell. Shell length 60 µm, shell width 20 µm, aperture diameter 8—10 µm.