Stephanoarcus vestibulis (Håkansson, Theriot & Stoermer) 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 : 3-4

Stephanoarcus vestibulis (Håkansson, Theriot & Stoermer) Genkal, Kulikovskiy, Glushchenko & Tseplik comb. nov. ( Figs 7–30 )

Basionym: Stephanodiscus vestibulis Håkansson, Theriot & Stoermer 1986 . Nordic Journal of Botany 6(4): 504, figs 1–10.

Synonyms: S. triporus sensu Genkal & Trifonova, 2006 , Table IV, 9; S. triporus sensu Genkal & Trifonova, 2009 , Table VIII, 3; S. triporus sensu Genkal & Kuzmin in Genkal 2013, Tab. IV, 1, 3; S. triporus sensu Genkal et al., 2011 , Table IV, 5, 6; S. triporus sensu Genkal & Belyaeva, 2011 , Tab. IV, 1–3.

Description. Cells single, low cylindrical. Valves circular, with a strongly convex or concave center, 4–13 µm in diameter, 11–16 striae in 10 µm, 33–37 areolae in 10 μm (n = 34). Interfascicles strongly raised on the outside, in highly silicified valves connected with crossbars. Fascicles consist of 1 areola at the center and 2–4 areolae towards the valve edge, areolae round to elliptic. In the center of the valve the areolae are arranged irregularly, often there is one larger areola and a single valve face fultoportula with 2–4 satellite pores. The spines are large and pointed, located on costae at the junction of valve face and mantle; density 14–18 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 with thickened edges and sometimes triangular or rounded flaps, located under each 2–5 spines; density 3.9–4.2 in 10 μm. A single sessile rimoportula with a long 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: Narva and Kama Reservoirs, Unezhma River and Lake Okunevo (Karelia), Delingde and Taz rivers

(Western Siberia).

Figures

FIGURES 7–12. Stephanoarcus vestibulis. Scanning electron microscopy, external views. Scale bars 1 μm.

FIGURES 13–18. Stephanoarcus vestibulis. Scanning electron microscopy. 13, 14. External views. 15–18. Internal views. Arch-like structures on valve mantle marked by white arrowheads. Scale bars 1 μm (13–15, 17, 18), 0.5 μm (16).

FIGURES 19–24. Stephanoarcus vestibulis. Scanning electron microscopy, external views. Arch-like structures on valve mantle marked by white arrowheads. Scale bars 1 μm.

FIGURES 25–30. Stephanoarcus vestibulis. Scanning electron microscopy. 25, 26. External views. 27–30. Internal views. Arch-like structures on valve mantle marked by white arrowheads. Scale bars 1 μm (25, 27–30), 0.5 μm (26).