Stephanoarcus triporus (Genkal & Kuzmin) 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

Stephanoarcus triporus (Genkal & Kuzmin) Genkal, Kulikovskiy, Glushchenko & Tseplik comb. nov. ( Figs 1–6 )

Basionym: Stephanodiscus triporus Genkal & Kuzmin 1978 . Botanicheskii Zhurnal 63(9): 1310, pl. 2: figs 1–8.

Synonyms: Stephanodiscus triporus var. volgensis Genkal in Genkal & Korneva 1990; Praestephanos triporus (Genkal & Kuzmin) Tuji & J.-S. Ki in Tuji et al. 2014.

Description. Cells single, low cylindrical. Valves flat or with a slightly convex or concave center, 3.7–14.5 µm in diameter, 10–30 striae, 23–61 areolae in 10 µm (n = 52). Fascicles consist of 1 areola at the center and 2–3 areolae towards the valve edge. In the center of the valve areolae are located irregularly, often there is one larger areola and 1, rarely 2 valve face fultoportulae with 2–4 satellite pores. Spines are small and pointed, located on each costa at the junction of valve face and mantle, sometimes absent; density 18–23 in 10 μm. Marginal fultoportulae with 3 satellite pores on the inside of the valve, on the outside opening into an arch-like structure at the edge of the valve, its opening varied from narrow to wide, sometimes with sector-shaped flaps, located under each 2–5 spines; density about 4.2–4.8 in 10 μm. A single sessile rimoportula with a long conical tube on the outside of the valve, located in the ring of spinules, and a labiate slit on the inside, oriented tangential to radial.

Ecology: Freshwater and brackish water plankton species.

Found in: Volga Reservoirs, Tsimlyanskoye and Revdinskoye Reservoirs (Middle Ural), Sestroretsky spill, Lake Verhnee Latvo ( Karelia), Lake Ladoga, Lake Baikal, rivers Nyukhcha and Shigerendzha ( Karelia), Oka, Izhora, Ob, Klyazma, Selenga, the Purparod Channel (Gydan Peninsula, Messoyakha river basin), Curonian Lagoon, Baltic Sea, Caspian Sea.

Figures

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.