Cryptodifflugia sacculus Penard, 1902

Diagnosis: Shell elongated, uncompressed, pyriform, with a very wide neck; slightly constricted posteriorly and widened at the aperture. When viewed from three‑quarters or from the front, the aperture appears to be surrounded by a collar, an optical impression caused by the widening of the neck. General form similar to Difflugia capreolata or D. rubescens. Shell wall organic, transparent, yellowish, varying from almost hyaline in young specimens to (rarely) golden‑brown in older ones. The chitinous membrane is always covered with foreign particles—siliceous amorphous fragments, small mineral grains, and very frequently diatoms, which may be as small as 5 μm.

Dimensions: Penard (1902): shell length 17–(20–23)–26 μm.
Own measurements: 14–25 μm.

Ecology: Freshwater; in Sphagnum and peat bogs, but also in other water types.

Distribution: Locally not rare.