Genus Playfairina Thomas, 1961
Diagnosis: Shell sub-cylindrical, narrowed at the region of the aperture, with circular or oval transversal section, when the shell is laterally compressed. The posterior end with caudal horn or rounded. The obliquely disposed round or oval aperture is with a brief evaginated collar. The shell is composed of endogenous round or oval siliceous plates of different diameter, with many small plates in the interstices between them. The collar is composed of 1-2 rows of smaller elliptical plates. The inside of the aperture is bordered by row denticulate apertural-plates. The filopodia are like those of Euglypha and Trinema.
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: Because of its small size, Playfairina valkanovi can often be overlooked or confused with T. lineare, but it is clearly distinguishable from the latter by its compressed shell, oval cross-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.