Cryptodifflugia sacculus Penard, 1902
Diagnosis: Shell colorless to brown, pyroid shaped with a distinct neck which widens towards the aperture; surface a rigid layer of organic material covered with some small xenosomes. Aperture terminal, circular and bordered by an usually somewhat thickened organic collar. Nucleus and pseudopodia as for the genus.
Dimensions: shell 20-28 µm.
Ecology: freshwater; in sphagnum and peat bogs, but also in other water types; locally not rare.