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.