Quadrulella variabilis Kosakyan et al., 2016

Description. Shell ovoid or pyriform, with a rounded posterior end, laterally compressed towards the pseudostome, very similar to that in Q. symmetrica, sometimes with an elongated neck. Shell colorless, composed of square plates, regularly arranged in rows. The plates are smaller near the aperture (3-4 µm), then gradually become larger (up to 7-9 µm ) toward the posterior end of the test. Aperture often curved and bordered by a thin organic lip.

Dimensions: According to Kosakyan et al. (2025): Shell length 66—69 (96) µm; width 35—40.5 (45) µm; aperture 17—18.5 µm wide (n=7). My measurements: Length 71 µm; aperture 17 µm wide; plates 3.4-9.4 µm.

Habitat: Sphagnum mosses.

Geographical distribution: Switzerland, Bulgaria, the Netherlands.

Remarks: The species has members with a variable neck length. The records from one location suggest rather a species complex than distinct intraspecific diversity.

References: Kosakyan, A., Lahr, D.J.G., Mulot, M., Meisterfeld, R., Mitchell, E.A.D., Lara, E., 2016. Phylogenetic reconstruction based on COI reshuffles the taxonomy of hyalosphenid shelled (testate) amoebae and reveals the convoluted evolution of shell plate shapes. Cladistics 32, 606–623. https://doi.org/10.1111/cla.12167