Acanthocystis lyra  Gerasimova & Plotnikov, 2016

Diagnosis: Cells are 21.0–30.0 μm (mean 26.0) in diameter. A cell coat consists of plate-scales of a single type, as well as long and short spine-scales. The spine-scales have cylindrical shafts, branching apices and circular basal plates with a clearly expressed marginal rim. The long spine-scales have a length 5.1–14.0 μm. The scale apices are divided into two pointed, deflected S-shaped branches 0.47–1.42 μm long. Both branches due to their curves form a lyrate distal end. The inner edge of each branch has 6–8 short teeth, whereas the outer edge is smooth. Basal plates of the long spine-scales are 0.6–1.5 μm. The short spine-scales are 1.9–3.7 μm long, broadly bifurcate at their apices. The scales possess marked primary and secondary bifurcations. Each apex of the secondary branch has two short teeth. Basal plates of the short spine-scales are 0.6–1.2 μm in diameter. The plate-scales are elliptical 2.4–4.1 × 1.4–2.5 μm, ornamented with an axial thickening in the central part.

Habitat: Freshwater. Type locality: Bottom sediment from the Pismenka River, Kidryasovo settlement, the South Urals, South- East of European part of Russia.

Remarks: A. cornuta Dürrschmidt, 1987 is similar to A. lyra in the structure of its long spine-scales. The spine-scales of A. cornuta are divided into two branches. Each branch has 2–4 teeth on the inner surface, whereas branches of A. lyra have 6–8 teeth on the inner surface. In addition, A. cornuta has spine-scales of one type and plate-scales ornamented with an axial thickening and radial ribs unlike A. lyra. Branching spine-scales are also known in A. bicornis Dürrschmidt, 1987. Long spine-scales of A. bicornis are divided into two branches. Each branch has a tooth on the inner surface, whereas branches of A. lyra has 6–8 teeth. Short spine-scales of A. bicornis with broadly bifurcate branches have two teeth of different length on the apices of each branch. In contrast to A. bicornis, the short spine-scales of A. lyra possess secondary bifurcation and two teeth at apices of the secondary branches. Plate-scales of both A. bicornis and A. lyra have a similar structure.