Argynnia lacustris Wailes, 1912*
Basionym: Argynnia dentistoma var. lacustris Wailes, 1912

Diagnosis: Shell pyriform, slightly elongated toward the pseudostome, which is proportionally small, crenulated, and abruptly truncated. Test very transparent, covered with siliceous, angular platelets and granules of various sizes, often intermixed with diatom frustules.

Dimensions: According to Wailes (1912): shell length 100 µm; width 80 µm; aperture 20 µm.
Other authors: length 120–206 µm, width 100–143 µm.
Specimens from a population in Killarney National Park, Ireland, measured 124–147 µm (Siemensma, 2026, unpublished).

Ecology: Sphagnum.

Remarks: *) Argynnia dentistoma var. lacustris Wailes, 1912 is correctly treated as Argynnia lacustris Wailes, 1912. A formal act is not required in this case according to the International Code of Zoological Nomenclature:
(1) Under Article 45.6.3, names published before 1961 using the abbreviation “var.” are deemed subspecific rather than infrasubspecific, and therefore constitute available species‑group names.
(2) Under Article 46.1, names established at either species or subspecies rank are simultaneously established at the other rank, with the same author and the same type. The authorship therefore remains unchanged.