Genus Playfairina Thomas, 1961
Diagnosis: Test sub-cylindrical, tapering a little towards the aperture, fundus rounded or terminating in a horn. Pseudostome and shell in transversal section circular. Shell composed of endogenous circular siliceous platelets, arrangement in most cases as in Trinema. Aperture invaginated, one row of denticulated marginal plates. Pseudopodia unknown, but due to the homologies in shell morphology Playfairina has filopodia.
Type species: Playfairina caudata Thomas, 1961
Ecology: sphagnum or humus.
Two species. Refs. Thomas (1961), Golemansky (1966).
Playfairina valkanovi Golemansky, 1966
Diagnosis: Shell colorless, transparent, elongate ovoid or retort shaped, laterally compressed, in cross-section oval; test with flat sole, slightly curved dorsal part and a rounded aboral region. Test composed of large, circular, incompletely overlapping plates and small oval plates between the large plates. Apertural region with brief evaginated collar, composed of one or two rows small elliptic or prolonged plates. Aperture oval, bordered by 12-18 denticulate apertural-plates, each of them with a sharp median tooth. Pseudopodia thin, long, straight, usually numerous, slow moving (after Todorov, 2019).
Dimensions: Length 36-45 µm; width 10-15 µm.
Ecology: Widely spread moss- and humus-dwelling, with preferences to high-mountain Sphagnum-habitats. Cosmopolitan.
Remarks: Due to its small size Playfairina valkanovi can often be overlooked or be confused with P. valkanovi, but when it is looked carefully is clearly distinguishable from the last by its compressed shell, oval transversal section, evaginated collar and oval aperture, smaller number of denticulate apertural plates (12-18) compared to T. lineare (18-28) (Todorov and Bankov, 2019).
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.