taxonID	type	description	language	source
03CA8782DF43C20FFF17F8D8FAF0FDFA.taxon	type_taxon	Type species (here designated): Stephanoarcus triporus (Genkal & Kuzmin) Genkal, Kulikovskiy, Glushchenko & Tseplik comb. nov.	en	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): 1-17, DOI: 10.11646/phytotaxa.712.1.1, URL: https://doi.org/10.11646/phytotaxa.712.1.1
03CA8782DF43C20FFF17F8D8FAF0FDFA.taxon	description	Description Cells low cylindrical to disc-shaped. The valves are circular, flat, convex or concave. Valve structure consisting of radial ribs or hyaline interfascicles and fascicles of areolae between them that consist of single areolae near the center, and 2 – 4 areolae per fascicle towards the edge of the valve. Fascicles continue onto valve mantle without significant change in structure of areolae. In the center of the valve there is one or several areolae located randomly; rarely the center is hyaline. Areolae are locular, with a foramen on the external surface of the valve, and a domed velum on the inside. Interfascicles usually end in spines or spinules at the junction between valve face and mantle, less often the spines are absent. Valves with a single valve face fultoportula with 2 – 4 satellite pores. Marginal fultoportulae have 3 satellite pores on the inside of the valve and open on the outside at the edge of the valve with an arch-like structure. A single rimoportula is located in the ring of spines, externally forming a tube and opening as a labiate slit internally.	en	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): 1-17, DOI: 10.11646/phytotaxa.712.1.1, URL: https://doi.org/10.11646/phytotaxa.712.1.1
03CA8782DF43C20FFF17F8D8FAF0FDFA.taxon	etymology	Etymology: The genus name reflects the presence of arch-like structures at the valve edge as one of the defining features and the similarity between the new genus and Stephanodiscus. This genus name is treated as masculine.	en	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): 1-17, DOI: 10.11646/phytotaxa.712.1.1, URL: https://doi.org/10.11646/phytotaxa.712.1.1
03CA8782DF40C20FFF17FD68FE9BFAE6.taxon	description	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.	en	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): 1-17, DOI: 10.11646/phytotaxa.712.1.1, URL: https://doi.org/10.11646/phytotaxa.712.1.1
03CA8782DF40C20FFF17FD68FE9BFAE6.taxon	biology_ecology	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.	en	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): 1-17, DOI: 10.11646/phytotaxa.712.1.1, URL: https://doi.org/10.11646/phytotaxa.712.1.1
03CA8782DF40C20EFF17FA54FED6FF50.taxon	description	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).	en	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): 1-17, DOI: 10.11646/phytotaxa.712.1.1, URL: https://doi.org/10.11646/phytotaxa.712.1.1
03CA8782DF45C204FF17F8FAFCD6FE1C.taxon	description	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.	en	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): 1-17, DOI: 10.11646/phytotaxa.712.1.1, URL: https://doi.org/10.11646/phytotaxa.712.1.1
03CA8782DF4BC207FF17FCB8FEC2FEC4.taxon	description	The arch-like structures around the marginal fultoportulae are quite diverse in their morphology (see schemes in Fig. 38). For example, in the type material of S. triporus arches with both wide and narrow openings were observed, sometimes with sector-shaped flaps visible on the sides of the arches (Kiss et al. 2013, Figs 8 – 9, 16); the same variability is shown in other studies (e. g., Tuji et al. 2014, Fig. 2 C; Houk et al. 2014, Pl. 155 Figs 7 – 10; Genkal et al. 2020, Table 63: 1 – 6 and others). In our material, we observed arches with varying width (Figs 1, 3). S. vestibulis is also a widely known species; the type population possesses medium width arches with thickened edges (Håkansson et al. 1986, Fig. 6, 8), and also rounded (Gotoh et al. 1998, Figs 2 – 9) or triangular (this study, Fig. 22) flaps were observed. The more recently described S. lacustris and S. hashiensis are characterised by arches with rounded (Houk et al. 2014, Plate 150 Fig. 2) and sector-shaped (Houk et al. 2014, Plate 151 Figs 11 – 13) flaps respectively, with very narrow arches being typical for S. hashiensis. Given the high variability of this feature, the defining characteristic of Stephanoarcus gen. nov. is the presence of the arch-like structure, not its shape. However, in future studies it would be very beneficial to research the patterns of this variability by observing populations from different geographic locations and cells in different stages of the life cycle, as well as using molecular genetic methods to determine the taxonomic significance of this feature. Molecular data obtained by Tuji et al. (2014) showed the close relationship between S. triporus and P. suzukii, however, this conclusion is not supported by morphological analysis, and the issue requires further research.	en	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): 1-17, DOI: 10.11646/phytotaxa.712.1.1, URL: https://doi.org/10.11646/phytotaxa.712.1.1
