Surirella liubingii J. Y. Long 2023, sp. nov

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