Playfairina valkanovi  Golemansky, 1966

Diagnosis: Shell colourless, transparent, elongate‑ovoid to retort‑shaped, laterally compressed; in cross‑section oval. Test with a flat ventral sole, a slightly curved dorsal side, and a rounded aboral region. Shell composed of large, circular, incompletely overlapping plates, with smaller oval plates filling the interstices. Apertural region with a short evaginated collar consisting of one or two rows of small elliptical or elongate plates. Aperture oval, bordered by 12–18 denticulate apertural plates, each bearing a sharp median tooth. Pseudopodia thin, long, straight, usually numerous and slow‑moving (after Todorov, 2019).

Dimensions: Golemansky (1966): shell length 36–45 µm; width 10–15 µm.

Ecology: Widely distributed in moss and humus; with a preference for high‑mountain Sphagnum habitats. Also recorded from sediment in a Croatian cave (2024).

Geographical distribution: Cosmopolitan.

Remarks: Due to its small size, Playfairina valkanovi is easily overlooked or confused with Trinema lineare. It is, however, clearly distinguishable by its compressed shell, oval cross‑section, evaginated collar, oval aperture, and the lower number of denticulate apertural plates (12–18) compared with T. lineare (18–28) (Todorov & Bankov, 2019).

References:
Golemansky, V. (1966). Playfairina valkanovi nov. sp, – Une nouvelle rhizopode d’eau douce (Rhizopoda, Testacea). Comptes Rendus de l’Académie Bulgare des Scienses. 19: 1.

Todorov, M. & Bankov, N. (2019). Morphological variability of testate amoebae (Amoebozoa: Arcellinida) from Bulgaria, with notes on diagnostic characters. Acta Zoologica Bulgarica, 71(2), 199–207

Remarks: I found this pretty vivid specimen in a sphagnum sample from the Hautes Fagnes (High Fenns) in Belgium. The nucleus was large and fully granular, which differs from the central nucleolus as described for T. lineare.