Acanthocystis tyrasiana  Zagumyonnyi & Tikhonenkov, 2022

Diagnosis: Cell diameter about 10 µm. Spine-scales 2.9–11.2 µm, consisting of a small circular basal plate, 0.61–1.08 µm wide and a hollow non-narrowing cylindrical shaft, 0.21–0.31 µm in diameter with 4, less frequently 3, short straight teeth at the top. Plate-scales oval, texture-less, 2.0–3.3x 1.1–2.4 µm. A short medial thickening is visible on a few scales.

Habitat: Type locality: Spring water in oak and hornbeam forest, Ukraine (48°28012.0600 N26°46013.9100 E).

Remarks: This species differs from A. taurica Mikrjukov, 1997 in the lower number of apical teeth on the spine-scales (4 rarely 3 in A. tyrasiana vs 5, rarely 4, 6 or 7 in A. taurica), longer spine-scales (2.3–11.2 µm vs x 4.2 mm), and in the absence of lateral deviation of the apical teeth. It differs from A. penardi by the lower number of apical teeth of spine-scales (4 rarely 3 vs 4–12); differs from A. spinosa Cavalier-Smith et von der Heyden, 2007 by the straight shafts and greater number of teeth on the apex (4 rarely 3 vs 3). It differs from Acanthocystis trifurca Nicholls, 1983 in the greater number and smaller size of the apical teeth (4, rarely 3 vs 3). It differs from A. quadrifurca Nicholls, 1983 in the smaller size of the apical teeth, the texture-less plate-scales, and the absence of radial slits.