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During our investigations on the freshwater diatoms from Qinghai Province, China, four sympatric Surirella taxa belonging to the group Pinnatae were analysed. Based on morphological observations derived from light and scanning electron microscopy, three of these four taxa were identified as: S. minuta, S. lacrimula, and S. brebissonii var. kuetzingii. The fourth taxon is described as Surirella liubingii sp. nov., a new species with a unique combination of characteristics. These include the distribution pattern of its costa-stria bundles (CSBs) alternating with its over-fibula costae (OFCs), which is formed by the distinctly elevated CSBs on the valve face, mostly composed of three costae, and OFCs with a remarkedly lower position. Other characteristics include the presence of robust fibulae extending to the valve midline, the presence of only one portula between two adjacent fibulae, and a “pseudoseptum” extending internally from the valve margin. From the observations on these four Surirella taxa, we described and discussed two types of fibula (one in which the fibula nearly reaches the valve midline and one with short fibula) and two types of portula morphology (one with only one portula between two adjacent fibulae and the other with 2–4 portulae between two adjacent fibulae).

Surirella brebissonii var. kuetzingii Krammer & Lange-Bertalot 1987 (LM: Figs 78–89, SEM: Figs 90–101, 106) Observations:— LM: Valve outline ovate to elliptical with broadly rounded headpole and narrowly rounded footpole. Valve dimensions (n = 25): 14–25 μm long, 6.9–8.8 μm wide (measured at widest part of the valve), length/width ratio 1.4–1.6. Valve composed of two portions: central portion and outside portion (indicated in Fig. 83). Costa-stria bundles (CSBs) visible, alternated with over-fibula costae (OFCs) from pole to pole. CSBs reaching valve margins. CSBs parallel at valve middle part, radiate approaching apices. Fibulae well-developed, spanning c. 1/4 of valve width, not extending to midline, 6–8 in 10 μm. SEM: Each CSB often composed of three costae and four striae (Figs 90–92). Striae multiseriate, composed of 3–5 rows of areolae, 23–25 in 10 μm (measured from SEM images, n = 4). Outside openings of areolae slit-like (Figs 92–95). Raphe canal located directly on mantle. Distal raphe endings simple and interrupting at both apices (Figs 93, 94, two arrows respectively). Internally, valve composed of two portions: central portion and outside portion (indicated in Fig. 97). Wall of raphe canal growing slightly into cell cavity leaving the portulae visible. Fibulae short, spanning c. 1/4 of valve width, not extending to valve midline (Figs 96–98). Raphe continuous at headpole (Fig. 99, wavy arrow), but interrupted at footpole (Fig. 100, two arrows). Three portulae produced between two adjacent fibulae (Figs 101, 106, three arrows). The areas between the fibulae form marginal trough-like depressions (Fig. 106). Ecology and distribution:— Epilithic in freshwater river. Surirella brebissonii var. kuetzingi was found in the same sampling site with S. liubingii, for the environmental parameters, see above. It is commonly found in Europe with reports from Germany, France and Poland (Krammer & Lange-Bertalot 1987, Bey & Ector 2013, Szczepocka et al. 2018).

Surirella lacrimula J.D. English 2012 (LM: Figs 55–66, SEM: Figs 67–77, 105) Observations:— LM: Valve outline ovate with broadly rounded headpole and cuneate footpole (Figs 55–66). Valve dimensions (n = 30): length 24–34 μm, width 10.3–13.1 μm (measured at the widest part of the valve), length/width ratio 2.1–2.6. Valve composed of two distinct portions: central portion and outside portion (indicated in Fig. 59). Fibulae evident, spanning c. 1/4 of valve width, not extending to midline, 7–9 in 10 μm. Fibulae parallel at valve middle, radiate approaching apices. SEM: Valve face flat making CSBs difficult to distinguish as CSBs not elevated from OFCs (Fig. 67–71). Striae multiseriate, composed of 3 or 4 rows of areolae, 30–32 in 10 μm (measured from SEM images, n = 4). Outside openings of areolae slit-like (Figs 68–71). Raphe canal located directly on mantle. Internally, valve composed of two portions: central portion and outside portion (indicated in Fig. 74). Wall of raphe canal growing slightly into cell cavity so that the portulae are easily visible (Figs 72–74). Fibulae short, a few bifurcate, spanning c. 1/4 of valve width, not extending to valve midline (Figs 72–74). Raphe continuous at headpole (Fig. 76, wavy arrow), but interrupted at footpole (Fig. 77, two arrows). One to three portulae occurring between two adjacent fibulae (Fig. 75, three arrows; Fig. 105, three arrows). Distribution:— S. lacrimula was found in the same site with S. liubingii. From the literature, this species appears to have a global distribution as it has been reported in the USA, France, Argentina, and Iran (English & Potapova 2012, Bey & Ector 2013, Seeligmann & Maidana 2019, Safiallah et al. 2020)., Published as part of Long, Ji-Yan, Liu, Bing, Rioual, Patrick, Yang, Bin & Zhou, Min, 2023, Ultrastructure of four Surirella taxa (Bacillariophyceae) from Qinghai Province, northwest China, with reference to the characteristics of portulae, pp. 163-177 in Phytotaxa 592 (2) on page 168, DOI: 10.11646/phytotaxa.592.2.11, http://zenodo.org/record/7840352, {"references":["English, J. D. & Potapova, M. G. (2012) Ontogenetic and interspecific valve shape variation in the Pinnatae group of the genus Surirella and the description of S. lacrimula sp. nov. Diatom Research 27 (1): 9 - 27. https: // doi. org / 10.1080 / 0269249 X. 2011.642950","Bey, M. - Y. & Ector, L. (2013) Atlas des diatomees des cours d'eau de la region Rhone-Alpes, Tome 6. Bacillariacees, Rhopalodiacees, Surirellacees. DREAL Rhone-Alpes, Lyon, France, pp. 973 - 1182.","Seeligmann, C. & Maidana, N. (2019) Diatomeas perifiticas de un rio de montana (Tucuman, Argentina). Lilloa 56 (1): 64 - 91. https: // doi. org / 10.30550 / j. lil / 2019.56.1 / 5","Safiallah, S., Saadatmand, S., Kheiri, S. & Iranbakhsh, A. (2020) Biodiversity of diatoms in the Kashkan River in the Zagros Mountains, western Iran. The Iranian Journal of Botany 26 (2): 141 - 161. https: // doi. org / 10.22092 / ijb. 2020.351698.1296"]}

Surirella liubingii J.Y.Long sp. nov. (LM: Figs 1–14, SEM: Figs 15–26, 102, 103) Observations:— LM: Valve outline long-ovate to ovate with broadly rounded headpole and cuneate footpole (Figs 1– 14). Valve dimensions (n = 21): length 22–33 μm, width 8.5–9.9 μm (measured at widest part of the valve), length/width ratio 2.3–3.7. Costa-stria bundles (CSBs) distinct, alternated with over-fibula costae (OFCs) from pole to pole. CSBs not reaching valve margins because the internal wall of raphe canal growing into cell cavity to form a “pseudoseptum” from the valve margin (indicated by two arrows in Fig. 4, see also Figs 21–23). CSBs parallel at the valve middle, slightly radiate approaching apices. Fibulae distinct, extending to midline, 6–7 in 10 μm. SEM: Each CSB mostly composed of three costae and four striae, but occasionally two costae and three striae or four costae and five striae (Figs 15–17). Tiny rib-like thickenings produced externally (Fig. 18, arrows). Striae multiseriate, composed of 3 or 4 rows of areolae, 24–26 in 10 μm (measured from SEM images, n = 3). Outside openings of areolae round to slit-like (Figs 18–20). Raphe canal located directly on mantle. Distal raphe endings simple and interrupting at both apices (Figs 19, 20, two arrows respectively). Internally, wall of raphe canal growing into cell cavity to the extent that the internal raphe canal wall is developed to form a longitudinal siliceous plate (a “pseudoseptum” from the valve margin, indicated by two double-headed arrows in Fig. 21), which hides the portula structure. The wall of the raphe canal is striated (Fig. 26). Fibulae robust, occasionally bifurcate, extending to valve midline (Figs 21–23, 25, 102). Raphe continuous at headpole (Fig. 24, arrow), but interrupted at footpole (Fig. 26, two arrows). One portula produced between two adjacent fibulae (Fig. 103, three arrows). Type:— CHINA, Qinghai province, Menyuan County: unnamed freshwater river course, sampling point 37°27'28" N, 101°23'15" E, 2940 m asl. Bing Liu, 18 th July 2019 (holotype slide JIU! DIA202315, specimen circled on slide = Fig. 1). Etymology:— Named after Dr. Bing Liu who is the first author’s supervisor and who collected the samples. Ecology and distribution:— Epilithic in river. The following environmental parameters were measured. Conductivity was 448 ± 1 μS̔cm –1, pH was 8.36 ± 0.03 and water temperature was 11.9 ± 0.5 °C. So far, Surirella liubingii has only been found in the type locality., Published as part of Long, Ji-Yan, Liu, Bing, Rioual, Patrick, Yang, Bin & Zhou, Min, 2023, Ultrastructure of four Surirella taxa (Bacillariophyceae) from Qinghai Province, northwest China, with reference to the characteristics of portulae, pp. 163-177 in Phytotaxa 592 (2) on pages 166-167, DOI: 10.11646/phytotaxa.592.2.11, http://zenodo.org/record/7840352

Surirella minuta Brébisson in Kützing 1849 (LM: Figs 27–42, SEM: Figs 43–54, 104) Observations:— LM: Valve outline long-ovate to ovate with broadly rounded headpole and cuneate footpole (Figs 27–42). Valve dimensions (n = 38): length 20–46 μm, width 8.4–11.0 μm (measured at widest part of the valves), length/width ratio 2.1–4.4. Costa-stria bundles (CSBs) evident, alternated with over-fibula costae (OFCs) from pole to pole. CSBs reaching valve margins. CSBs parallel at valve middle, radiate approaching apices. Fibulae evident, nearly extending to midline, 7–9 in 10 μm. SEM: Each CSB mostly composed of three costae and four striae, or two costae and three striae (Figs 43–46). Striae multiseriate, composed of 3–5 rows of areolae, 25–27 in 10 μm (measured under SEM images, n = 3). Outside openings of areolae slit-like (Figs 45–48). Raphe canal located directly on mantle. Distal raphe endings simple and interrupting at both apices (Figs 47, 48, two arrows respectively). Internally, wall of raphe canal only slightly growing into cell cavity such as the portulae are visible (Figs 49, 50, 54, 104). Fibulae medium-sized, occasionally bifurcate, extending to valve midline (Figs 49–51). Each fibula corresponds to a sinking in the mantle (Fig. 51). Raphe continuous at headpole (Fig. 52, wavy arrow), but interrupted at footpole (Fig. 53, two arrows). One portula produced between two adjacent fibulae (Fig. 54, two arrows, Fig. 104, three arrows). Distribution:— Surirella minuta was commonly found and was dominant in the assemblages collected on the stone surfaces in the river course. It was associated with S. liubingii, S. lacrimula and S. brebissonii var. kuetzingi. From the literature, this species has a global distribution (Krammer & Lange-Bertalot 1987, English & Potapova 2012, Bey & Ector 2013, Dedić et al. 2015, Caglar et al. 2022)., Published as part of Long, Ji-Yan, Liu, Bing, Rioual, Patrick, Yang, Bin & Zhou, Min, 2023, Ultrastructure of four Surirella taxa (Bacillariophyceae) from Qinghai Province, northwest China, with reference to the characteristics of portulae, pp. 163-177 in Phytotaxa 592 (2) on page 168, DOI: 10.11646/phytotaxa.592.2.11, http://zenodo.org/record/7840352, {"references":["Kutzing, F. T. (1849) Species algarum. Lipsiae [Leipzig]: F. A. Brockhaus. pp. [i] - vi, [1] - 922.","Krammer, K. & Lange-Bertalot, H. (1987) Morphology and taxonomy of Surirella ovalis and related taxa. Diatom Research 2 (1): 77 - 95. https: // doi. org / 10.1080 / 0269249 X. 1987.9704986","English, J. D. & Potapova, M. G. (2012) Ontogenetic and interspecific valve shape variation in the Pinnatae group of the genus Surirella and the description of S. lacrimula sp. nov. Diatom Research 27 (1): 9 - 27. https: // doi. org / 10.1080 / 0269249 X. 2011.642950","Bey, M. - Y. & Ector, L. (2013) Atlas des diatomees des cours d'eau de la region Rhone-Alpes, Tome 6. Bacillariacees, Rhopalodiacees, Surirellacees. DREAL Rhone-Alpes, Lyon, France, pp. 973 - 1182.","Dedic, A., Plenkovic-Moraj, A., Kralj Borojevic, K. & Hafner, D. (2015) The first report on periphytic diatoms on artificial and natural substrate in the karstic spring Bunica, Bosnia and Herzegovina. Acta Botanica Croatica 74 (2): 393 - 406. https: // doi. org / 10.1515 / botcro- 2015 - 0029","Caglar, M., Bulut, H. & Selamoglu, Z. (2022) Epipsammic diatom fauna of Karabey Creek in Turkiye. Survey in Fisheries Sciences 9 (1): 65 - 77. https: // doi. org / 10.18331 / SFS 2022.9.1.6"]}

Oricymba fanjingensis Bing Liu & Rioual sp. nov. (LM: Figs 40–53, SEM: Figs 54–71) Description:— LM: Valves asymmetric to apical axis, dorsiventral with dorsal margin a little more arcuate than ventral margin (Figs 40–53). Apices apiculate. Valve dimensions (n = 36): 34–59 μm long, 9.9–14.6 μm wide, length/width ratio range 3.2–4.7, median 4.0. Axial area narrow, rhombic-lanceolate, expanded at oval central area. Raphe filiform. Proximal raphe endings deflected towards ventral side. Central pores present. Central area asymmetrical, small, occupying c. 1/4 of the valve width, flanked by c. 3 or 4 shortened ventral striae and 1 or 2 shortened dorsal striae. A stigma evident on ventral side of valve. Striae slightly radiate throughout valve, 8–10 in 10 μm in central portion of dorsal side, 7–11 in 10 μm in central portion of ventral side. Areolae easily resolved under LM, 20–24 in 10 μm. SEM, external view: Valves asymmetric along apical axis, proximal raphe endings clearly bent towards ventral side, and distal raphe fissures deflected towards dorsal side (Figs 54, 60–62). Marginal ridges evident along both dorsal and ventral valve margins (Fig. 54, four arrows; Figs 55–57, two arrows). Two valve surface ridges produced (Fig. 54, four wavy arrows; Figs 55–57, two wavy arrows), each parallel to each marginal ridge, thus two grooves formed (Figs 55–57, 63–65, two double-headed arrows). External openings of areolae mostly slit-like. Dentate projections produced under each external opening of areola. Apical pore field forming a continuous area, not divided by distal raphe fissure, clearly separated from areolae (Figs 58, 59), composed of c. 5–8 transapical rows and 12–14 pervalvar rows. Foramina of apical pore field mostly rounded, a notch on dorsal side of distal raphe fissure is present (Figs 58, 59, arrow, respectively). Valve mantle deep, meeting valve face at a right angle (Figs 66, 67). Striae continuing onto valve mantle, but terminated before mid-line of valve mantle, such that abvalvar part of mantle without ornaments. SEM, internal view: Valve slightly asymmetric along apical axis with apiculate apices, raphe straight, almost along the valve mid-line, virgae and depressed striae alternate throughout valve (Figs 66, 67). Proximal raphe endings not visible because obscured by flap above central nodule (Fig. 68, wavy arrow) and distal raphe ends terminating in knob-like helictoglossae (Figs 69–71). Internally, stigma having two slit-like openings, both with fine ingrowths from perimeter (Fig. 68, two arrowheads). Areola internal openings occluded by dentate projections (Figs 68–70). Apical pore field clearly separated from other parts of valve (Fig. 71). Type:— CHINA. Guizhou Province: Jiangkou County, sampling point from a headwater stream that runs into the Dajiang River (27°49′48″ N, 108°45′53″ E, 500 m asl), Bing Liu, December 31 st 2015 (holotype JIU! Slide DIA202202, specimen circled on slide = Fig. 40). Registration: http://phycobank.org/103644. Etymology:— Named after Fanjing Mountain, where the species was found. Ecology:— Inhabiting surfaces of submerged stones, thus, belonging to river epilithon. In fresh waters, detailed information in Table 1. This species was associated with Achnanthidium sinense Bing Liu & Blanco (in Liu et al., 2016: 195), A. minutissimum (Kützing) Czarnecki (Czarnecki 1994: 157), and several unidentified species of Ulnaria (Kützing) Compère (2001: 100) and Encyonema Kützing (1834: 529)., Published as part of Yuan, Li, Liu, Bing, Rioual, Patrick, Yi, Man-Qi & Zheng, Yan, 2023, Two new species of Oricymba (Bacillariophyta) from China, described with reference to the structure of the apical pore field, pp. 181-195 in Phytotaxa 591 (3) on page 188, DOI: 10.11646/phytotaxa.591.3.1, http://zenodo.org/record/7800808, {"references":["Liu, B., Blanco, S., Long, H., Xu, J. & Jiang, X. (2016) Achnanthidium sinense sp. nov. (Bacillariophyta) from the Wuling Mountains Area, China. Phytotaxa 284 (3): 194 - 202. http: // dx. doi. org / 10.11646 / phytotaxa. 284.3.4","Czarnecki, D. B. (1994) The freshwater diatom culture collection at Loras College, Dubuque, Iowa. Memoirs of the California Academy of Sciences 17: 155 - 174.","Compere, P. (2001) Ulnaria (Kutzing) Compere, a new genus name for Fragilaria subgen. Alterasynedra Lange-Bertalot with comments on the typification of Synedra Ehrenberg. In: Jahn, R., Kociolek, J. P., Witkowski, A. & Compere, P. (Eds.) Lange-Bertalot Festschrift. Studies on diatoms dedicated to Prof. Dr. Dr. h. c. Horst Lange-Bertalot on the occasion of his 65 th birthday. A. R. G. Gantner Verlag K. G., Ruggell, pp. 97 - 101."]}

Oricymba sinensis Bing Liu & Rioual sp. nov. (LM: Figs 1–15, SEM: Figs 16–39) Description:— LM: Valves dorsiventral possessing arcuate dorsal margin and slightly convex to straight ventral margin (Figs 1–15). Apices not protracted or occasionally slightly protracted, bluntly rounded. Valve dimensions (n = 31): 36–52 μm long, 7.8–10.1 μm wide, length/width ratio range 4.2–5.5, median 4.9. Axial area narrow, lanceolate, expanded at central area. Raphe filiform. Proximal raphe endings deflected towards ventral side (primary side). Central pores present. Central area asymmetrical, occupying c. 1/3 of the valve width, flanked by c. 4 shortened ventral striae. A stigma evident on ventral side of valve. Striae radiate throughout valve, 9–11 in 10 μm in central portion of dorsal side, 9–12 in 10 μm in central portion of ventral side. Areolae difficult to resolve under LM. SEM, external view: Valves asymmetric along apical axis, proximal raphe endings bent towards ventral side, and distal raphe fissures deflected towards dorsal side (Figs 16, 22, 28). Marginal ridge evident along dorsal valve margin (Figs 16–18, 20, black arrows, see also Figs 22–24, 26) whereas marginal ridge inconspicuous along the ventral margin (Figs 28–30, 32, black arrows). External openings of areolae slit-like except those adjacent to axial area, which are curved or lunate (Figs 23, 24, 26, arrows). Dentate projections produced under each external opening of areola. Areola density 30–35 in 10 μm. Shallow depressions present in axial and central area (Fig. 17, white arrows). Apical pore field forming a continuous area, not divided by distal raphe fissure, clearly separated from areolae (Figs 19, 21), composed of c. 5–8 transapical rows and 15–17 pervalvar rows. Foramina of apical pore field mostly rounded but a few top foramina elongate (Figs 25, 27, 31, 33, arrows). A notch present on dorsal side of distal raphe fissure (Figs 19, 21, 31, 33, wavy arrows, respectively). Valve mantle deep, meeting valve face at a right angle. Striae continuing onto valve mantle, but terminated before mid-line of valve mantle, such that abvalvar part of mantle without ornaments (Figs 20, 21, 29, 30, 32, double-headed arrows, respectively). Girdle bands simple, c. three copulae per cell (Fig. 21). SEM, internal view: Valve asymmetric along apical axis, raphe straight, almost along valve mid-line, virgae and depressed striae alternate throughout valve (Fig. 34). Proximal raphe endings not visible because obscured by flap above central nodule (Fig. 35, two wavy arrows) and distal raphe ends terminating in knob-like helictoglossae. Internally, stigma having two slit-like openings with fine ingrowths from perimeter (Fig. 35, two arrows). Areola internal openings occluded by dentate projections (Figs 35, 36, 38). Apical pore field clearly separated from other parts of valve (Fig. 37, two arrows). An undulate flap-like silica strip covering internal apertures of each pervalvar row of foramina, not completely occluding internal apertures (Fig. 39, two arrows). Type:— CHINA. Hunan province: Jianghua County, a sampling point from a headwater stream that runs into the Xiao River (25°4′24″ N, 111°50′54″ E, 380 m asl), Bing Liu, October 4 th 2021 (holotype JIU! Slide DIA202201, specimen circled on slide = Fig. 1). Registration: http://phycobank.org/103643. Etymology:— Named after China where the species was found. Ecology:— Inhabiting surfaces of submerged stones, thus, belonging to river epilithon. In fresh waters, detailed information in Table 1. This species was associated with Amphipleura vavilovii Glushchenko & Kulikovskiy (2017: 17), and several unidentified species of Fragilaria Lyngbye (1819: 182), Navicula Bory (1822: 128), Cymbella Agardh (1830: 1) and Gomphonema Ehrenberg (1832: 87)., Published as part of Yuan, Li, Liu, Bing, Rioual, Patrick, Yi, Man-Qi & Zheng, Yan, 2023, Two new species of Oricymba (Bacillariophyta) from China, described with reference to the structure of the apical pore field, pp. 181-195 in Phytotaxa 591 (3) on pages 183-188, DOI: 10.11646/phytotaxa.591.3.1, http://zenodo.org/record/7800808, {"references":["Glushchenko, A. M. & Kulikovskiy, M. S. (2017) Amphipleura vavilovii: A new diatom species of the family Amphipleuraceae from Laos [J]. Inland Water Biology 10 (1): 17 - 21. https: // doi. org / 10.1134 / S 1995082916040064","Lyngbye, H. C. (1819) Tentamen Hydrophytologiae Danicae Continens omnia Hydrophyta Cryptogama Daniae, Holsatiae, Faeroae, Islandiae, Groenlandiae hucusque cognita, Systematice Disposita, Descripta et iconibus illustrata, Adjectis Simul Speciebus Norvegicis. Hafniae, Typis Schultzianis, in commissis Librariae Gyldendaliae, Copenhague, 248 pp.","Bory de Saint-Vincent, J. B. G. M. (1822) Bacillariees. Dictionnaire Classique d'Histoire naturelle 2: 127 - 129.","Agardh, C. A. (1830) Conspectus criticus diatomacearum. Part 1. Litteris Berlingianis, Lund, 16 pp.","Ehrenberg, C. G. (1832) Uber die Entwickelung und Lebensdauer der Infusionsthiere; nebst ferneren Beitragen zu einer Vergleichung ihrer organischen Systeme. Abhandlungen der Koniglichen Akademie Wissenschaften zu Berlin, Physikalische Klasse, pp. 1 - 154."]}