Difflugia globulosa (Dujardin, 1837) Penard, 1902
Diagnosis: Shell brown, spherical or hemispherical, usually composed of large quartz particles but may also include diatom frustules; general appearance rough, although some smoother forms have been seen; aperture circular and surrounded by smaller particles which often appear smooth due to the overlaying cement; variation in this species is prolific, both in the composition of the shell and the size of the aperture in relation to the diameter of the shell.
Dimensions: Literature: diameter of shell 91-155 µm (Dujardin: 100-250 µm, see remarks below).
Ecology: Freshwater. Peatbogs, between wet sphagnum; oligotrophic ponds.
Remarks: Shells of this species can be confused with those of Phryganella nidulus which are more flattened.
Penard (1902) described this species as having two distinct forms, the typical form and one varying between 135 and 155 µm. He also described two smaller forms 50 to 70 µm in size. Cash et al. (1909) described a small form (15-50 µm) under the name D. globulus, and suggested that Dujardin’s original description of D. globulosa was ambiguous. Dujardin described this species as spherical or ovoid and 100-250 µm large. Probably he observed at least two different species.