Surirella liubingii J.Y.Long, 2023

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, Phytotaxa 592 (2), pp. 163-177 : 166-167

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.

Figures

FIGURES 1–14. Surirella liubingii sp. nov., LM (1000×). Fourteen different valves showing the size diminution series of this species. Note that the costa-stria bundles (CSBs) do not reach the valve margins because the internal wall of the raphe canal grows into the cell cavity to form a “pseudoseptum” from the valve margin (indicated by two arrows in Fig. 4). Fig. 1 corresponds to holotype specimen. Scale bar = 10 μm (in Fig. 1).

FIGURES 15–20. Surirella liubingii sp. nov., SEM, external view. 15–17. Three valves showing the valve shape, the pattern of costa-stria bundles (CSBs, white arrows labeled in Fig. 16) alternated with over-fibula costae (OFCs, black arrows labeled in Fig. 16) from pole to pole. 18. Middle section of the valve, detail from Fig. 17, note CSBs, OFCs, and multiseriate striae. 19, 20. Details of the valve apices from Fig. 17, note the simple, interrupted raphe endings at both the footpole (Fig. 19, two arrows) and headpole (Fig. 20, two arrows).Scale bars = 5 μm (Figs 15–17), 1 μm (Figs 18–20).

FIGURES 21–26. Surirella liubingii sp. nov., SEM, internal view. 21–23. Three complete valves, note the robust fibulae and the internal wall of the raphe canal that distinctly grows into the cell cavity to the extent that the internal raphe canal wall develops to form a longitudinal siliceous plate (i.e., a “pseudoseptum”) from the valve margin, indicated by two double-headed arrows in Fig. 21), which hides the portula structure. 24. Headpole from Fig. 21, note the continuous raphe. 25. Middle part, detail from Fig. 21, note the robust fibulae extending to the midline (two arrows) and multiseriate striae. 26. Footpole from Fig. 21, note interrupted raphe endings (two arrows) and striated raphe canal wall (two wavy arrows). Scale bars = 5 μm (Figs 21–23), 1 μm (Figs 24–26).

FIGURES 102–107. Characteristics of the portulae among five Surirella taxa, SEM, internal view. 102, 103. Portula structure of S. liubingii, note the striated internal raphe canal wall (Fig. 102, three arrows) and the presence of only one portula between two adjacent fibulae (Fig.103, three arrows). 104.Portula structure of S. minuta, note the occurrence of only one portula (three arrows). 105–107.Portula structure of S. lacrimula, S. brebissonii var. kuetzingii, and S. tientsinensis, respectively. Note that these three taxa have three portulae between two adjacent fibulae (three arrows respectively) but that a marginal trough-like depression is only produced in S. brebissonii var. kuetzingii (Fig. 106). Scale bars =1 μm (Figs 102–107).