Two new species of centrohelids Acanthocystis lyra sp. nov. and A. siemensmae sp. nov. from the Pismenka River in the South Urals, Russia, have been studied with scanning electron microscopy. Cells of these species have both long and short spine scales with hollow shafts and circular basal plates. A. lyra has the long spine scales divided into two curved S-shaped branches possessing small teeth on their inner surface. The short spine scales have primary and secondary bifurcations. Every secondary branch ends with two teeth. A. siemensmae has both long and short scales with funnel-like apices, which possess small teeth. Based on the scale morphology A. lyra has been attributed to the A. turfacea species group, whereas A. siemensmae has been attributed to the A. pectinata species group, both according to classification proposed by Mikrjukov, 1997. Similarities and differences of the new species with other members of the genus Acanthocystis have been discussed.
