Stephanoarcus lacustris (Klee & Houk) Genkal, Kulikovskiy, Glushchenko & Tseplik, 2025

Genkal, Sergei, Glushchenko, Anton, Tseplik, Natalia & Kulikovskiy, Maxim, 2025, A reinvestigation of Stephanodiscus triporus (Stephanodiscaceae, Mediophyceae) with the description of Stephanoarcus gen. nov., Phytotaxa 712 (1), pp. 1-17 : 8-10

Stephanoarcus lacustris (Klee & Houk) Genkal, Kulikovskiy, Glushchenko & Tseplik comb. nov. ( Figs 31–36 )

Basionym: Stephanodiscus lacustris Klee & Houk in Houk et al. 2014. Fottea (Supplement) 14: 45, pl. 150: figs 1–12.

Synonyms: S. triporus var. volgensis sensu Genkal & Korneva, 1990 , Fig. 4 f, g; S . triporus var. volgensis sensu Genkal 1992, Table XII, 5, XIII, 2, 3; S. triporus sensu Genkal, 2013 , Tab. I, 6; S. triporus sensu Genkal & Trifonova, 2011 , Tab. VI, 2, 3; S. triporus sensu Genkal et al., 2020 , Tab. 63, 3, 4.

Description. Cells low cylindrical. Valves flat or with a slightly convex or concave center, 3.1–8.0 µm in diameter,

10–20 striae, 31–56 areolae in 10 µm (n = 21). Fascicles consist of 1 areola at the center and 2–4 areolae towards the valve edge. In the center of the valve the areolae are located irregularly, often there is one larger areola in the center and a single valve face fultoportula with 2–4 satellite pores. Small conical spines located on costae at the junction of valve face and mantle, density 20–23 in 10 μm. Marginal fultoportulae with 3 satellite pores on the inside of the valve, on the outside opening at the edge of the valve into an arch-like structure, located under each 2–5 spines; density approximately 3.9 in 10 μm. A single sessile rimoportula with a conical tube on the outside of the valve, located in the ring of spines, and a labiate slit on the inside, oriented tangential to radial.

Found in: Neva Bay, Rybinsk and Cheboksary Reservoirs.

Figures

FIGURES 31–36. Stephanoarcus lacustris. Scanning electron microscopy. 31, 32. External views. 33–36. Internal views. Arch-like structures on valve mantle marked by white arrowheads. Scale bars 1 μm (31–35), 0.5 μm (36).

FIGURES 1–6. Stephanoarcus triporus. Scanning electron microscopy. 1–3. External views. 4–6. Internal views. Arch-like structures on valve mantle marked by white arrowheads. Scale bars 1 μm.