Gliwiczia skvortzowii Kulikovskiy, Lange-Bertalot & Witkowski 2013, sp. nov.

Frustules with a horse shoe-like internal cavum at both raphe and rapheless valve as characteristic of the genus. Valves broadly elliptical with broadly to weakly cuneately rounded ends. Length 12–24 µm, breadth 8–13 µm.

LM, raphe valve (Figs 20–32): Raphe filiform, straight, external central ends slightly expanded, distal ends shortly indistinctly deflected. Axial area narrow, linear, proximally broadening into a deltoid shape. Central area rhombi at the central nodule forming ca. 1.5 µm broad stauros to the valve margin unilaterally; on the opposite side the stauros appears interrupted by the elliptical cavum, at the margin (but see SEM, external view Figs 33, 34). Striae 24–25 in 10 µm, radiate throughout with several intercalated short ones at the margins proximally. Areolae punctate, ca. 30 in 10 µm.

LM, rapheless valve (Figs 1–19): Axial and proximal central area rhombic-lanceolate; central area forming a stauros unilaterally which appears obscured on the opposite side by an elliptical cavum. Striae ca. 24 in 10 µm, becoming progressively radiate from proximal towards distal part of the valve; no shorter striae intercalated at margins. Areolae irregularly spaced, considerably coarser than in raphe valves, 15–18 in 10 µm. SEM, raphe valve, external view (Figs 33–36): Raphe with small external central pores and distal ends more or less distinctly to opposite sides deflected. Distal ends may be pore-like expanded at a junction between the valve face and the mantle. The stauroid central area appears clearly asymmetrical becoming expanded towards the margin at that side where the cavum lies internally. Areola foramina are circular and open.

SEM, raphe valve, internal view (Figs 37–40): Central raphe ends deflected clearly to opposite sides as generally characteristic for achnanthoid and cocconeoid monoraphid genera. The stauros together with the raphe sternum is strongly elevated above the internal valve surface. The conspicuous cavity is opened by a relatively small aperture. Areolae uniseriate, small, approximately circular. Occlusion membranes visible or destroyed.

SEM, rapheless valve, internal view (Figs 41–42): The relief-like appearance of the rhombical sternum, stauros and cavum generally as in the raphe valve. Areola pattern differs from raphe valves by larger apertures lying in crater-like depressions, becoming smaller and transapically elongated at valve mantles. Occlusion membranes have become corroded more or less strongly.

Type: slide no. 15645m (holotypus here designated see Fig. 2) in collection Maxim Kulikovskiy, I.D. Papanin Institute for Biology of Inland Waters, Russian Academy of Sciences (IBIW) 20.07.1965, leg. A.P. Skabitschewsky.

Isotype: slide no. 15645a in collection Andrzej Witkowski, Institute of Marine Sciences, University of Szczecin (SZCZ).

Distribution: As yet known only from the Lake Baikal.

Etymology: This species dedicated to Boris Skvortzow one of the pioneers of the diatomological studies in Lake Baikal.