Pyxidicula spec.
Diagnosis: In a sample from a Mongolian fen (Łuców et al., 2025), we identified several shells resembling Pyxidicula ornata. These shells shared some morphological characteristics with P. ornata—such as a membranous shell, building units, the same color, and a broad rim—but the shells were relatively less domed compared to those of P. ornata and differed significantly in size (diameter: 51—87 μm vs. 139—163 μm for P. ornata) and in the absence of dents. The height ranged from 30—39 μm, and the rim was 8.4—11.0 μm wide (n = 21). The building units measured 0.6—0.9 μm in diameter. No living specimens were observed.
We examined 21 specimens using LM and 3 specimens with SEM. These shells may represent a new species, a variety, or smaller specimens of P. ornata. In our publication, we referred to this taxon as Pyxidicula cf. ornata. A similar, likely identical, species was reported in Canada by Davies et al. (2024); see the plate at the bottom.
In the same sample, we also found empty shells of P. cymbalum (diameter: 56—93 μm; building units: 0.9—1.1 μm across; rim: 7.4—8.8 μm wide). The color of these shells was distinctly different from the other two Pyxidicula taxa in the sample.
Dimensions: According to Łuców et al. (2025): Shell diameter 51—87 µm, mean 74.5; SD 8.7 (n=24).
Ecology: Fen, Mongolia
