Playfairina caudata (Playfair, 1917) Thomas, 1961
Basionym: Trinema caudatum Playfair, 1917

Diagnosis: Shell subcylindrical, tapering toward the apertural region, with a circular to oval transverse section when laterally compressed. Posterior end rounded or bearing a caudal horn. Aperture oblique, circular or oval, with a short evaginated collar. Shell composed of endogenous round or oval siliceous plates of varying diameter, with numerous small plates filling the interstices. The collar consists of one to two rows of smaller elliptical plates. The inner margin of the aperture is bordered by a row of denticulate apertural plates. Filopodia similar to those of Euglypha and Trinema.

Measurements: Playfair (1917): shell length 100 µm, width 25 µm, aperture diameter 15 µm, tail 27 µm, scales 5 µm.
Jung (1942): length 68 µm, width 25 µm, aperture 12 µm.
Thomas (1961): British population: length 50–60 µm, width 15–18 µm, aperture 5–7 µm; French population approx. 35 µm long.

Ecology: Sphagnum and humus.

Remark: The large size differences between populations suggest that more than one species may be involved.

References:
Playfair, G. I. (1917). The Protozoa of the moss Sphagnum. Proceedings of the Linnean Society of New South Wales, 42, 633–675. Thomas, R. (1961). Playfairina caudata n. g., n. sp., un nouveau Thécamoebien du sol. Revue de Zoologie et de Botanique Africaines, 64(1–2), 1–6.