Cryptodiffflugia crenulata Playfair, 1917
Syn.: Difflugiella crenulata Grospietsch, 1964
Syn.: Difflugiella crenulata Schönborn, 1965

Diagnosis: Shell ovoid, with a truncate base, sometimes slightly constricted above the base to form an obscure neck; end‑view circular and crenulated. Shell membrane smooth, thick, chitinous, hyaline or pale yellow, indented throughout so that the test appears broadly crenulated in optical section, both front and end. Aperture circular, simple, slightly smaller than the base. Nucleus spherical. Cell sometimes containing one or two large bipyramidal crystals.

Dimensions: Playfair: length 17–20 µm, breadth 14–16 µm.
Other authors: length 15–20 µm; width 10–16 µm; aperture diameter 4 µm.
Own measurements: length 15–18 µm.

Ecology: Freshwater; on submerged aquatic plants; also in Sphagnum mosses.

Distribution: Cosmopolitan; not rare.