Phryganella nidulus Penard 1902
Diagnosis: Shell large, usually of rough contour, brown, opaque, circular and hemispherical in lateral view, usually composed of a mixture of diatom frustules and quartz particles; one or more large particles contributes to the irregular outline of the shell and aperture; aperture large and slightly invaginated; pseudopodia slender, but often accompanied by broad lobes of protoplasm extending radially in all directions.
Dimensions: Penard 165-220 µm in diameter; my measurements 140 µm.
Ecology: fresh water and mosses. I found shells of this species only in oligotrophic ponds, where it was not rare, but you have to see living specimens to be sure of a positive identification.
Remarks: Animal very shy; without an examination of the living organism, the identification of the shell alone is not possible. Shells of this species might be confused with those of Difflugia lithoplites and Difflugia globulosa.