Acanthocystis kirilli  Zlatogursky, 2010

Diagnosis: Cell body ca. 9 µm in diameter; including scales about 17 µm. Axopodia ca. 28 µm long. Tangential plate-scales are oviform and slightly punctuated. Length of the plate-scales is 2.3-2.7 µm, width is 1.6-1.8 µm. Radial spine-scales are slightly branched on the distal end. Length of the spine-scales is 2.6-7.6 µm, thickness 0.2-0.3 µm. Cells actively move on the bottom of the culture dish or float in the culture medium.

Differential diagnosis. Acanthocystis kirilli has branching radial scales. Branching scales are also known in A. turfacea, A. astrakhanensis, A. cornuta, and A. bicornis. However, in Acanthocystis turfacea and in A. bicornis each cell has two types of radial scales, while in A. kirilli only one type was found. In A. cornuta both branches of the radial scales have small teeth, while in A. kirilli these branches are smooth. In A. astrakhanensis radial scales have massive, broad furcation, resembling a boomerang or a crescent. They may be described as broad flattened blades, exceeding the diameter of the shaft of the radial scale. Quite the contrary, in A. kirilli these branches are small, and do not protrude from the radial scale shaft edge. It looks rather like the upper half of the letter X than like a crescent.
Type location. Symniakhovskoe lake, Valamo island, North-Western Russia, N 61122,9390 E 30158,4200.