Surirella brightwellii W. Smith. Both 1853

Surirella brightwellii W. Smith 1853 Figs 1, 2, 3 Description. LM (Fig. 1). Valve outlines ovate with broadly rounded headpole and cuneate footpole (Fig. 1). Valve dimensions (n = 102): length range 19–56 μm, width range 13–29 μm at its widest region. Costa-stria bundles (CSBs) distinct, alternating with over-fibula ribs (OFRs) from pole to pole (labelled in Fig. 1 F). CSBs parallel at the valve middle, radiate approaching two apices. Fibulae visible, short (judged by OFRs, labelled in Fig. 1 F), 5–7 in 10 μm. SEM (Figs 2, 3). Externally, raphe canal located directly on the mantle, and wall of raphe canal hyaline (Fig. 2 A, B), distal raphe endings straight, interrupted at both headpole and footpole (Fig. 2 D, E). Surface costae mostly raised, some reaching valve midline (Fig. 2 C). Each CSB composed of ca. 2–4 costae and 3–5 striae (Fig. 2 F). Outside openings of areolae slit-like or rounded (Fig. 2 D, E). Striae multiseriate, composed of ca. 2–5 rows of areolae (Fig. 2 D, E), 19–22 in 10 μm (measured at the valve margin from SEM images, n = 4). Surface siliceous warts and reticulate thickenings produced on costae and between adjacent two costae, respectively (e. g., Fig. 2 D, E). Internally, wall of raphe canal not growing conspicuously into cell cavity, leaving portulae visible (Fig. 3 A, B). Fibulae slim, short, sometimes doubled (Fig. 3 B, arrows), spanning ca. 1 / 4 of valve width, not extending to valve midline except at two valve poles. Marginal trough-like depressions present around entire raphe canal (Fig. 3 A, black dotted lines). Raphe continuous at headpole (Fig. 3 C, arrow) whereas interrupted at footpole (Fig. 3 D, two arrows). 2–5 portulae produced between two adjacent fibulae (Fig. 3 F, arrows). Inner openings of areolae rounded, not rimmed. Each mantle sinking against a fibula (Fig. 3 E, arrows). Ecology and distribution. The type localities of Surirella brightwellii are the coasts of Norfolk and Lewes (United Kingdom), and Smith stated that it was a fresh or brackish water species (Smith 1853). According to Krammer and Lange-Bertalot (1987), the syntypes designated by Hoover (1976) originate from a locality in Sussex (a brackish habitat). In this study, Surirella brightwellii was found to be a dominant species in the benthic diatom community in Lake Qinghai. At the sampling point where it was collected near the lakeshore of Lake Qinghai (36°50'34"N, 99°42'39"E, 3210 m asl.) on July 19, 2019, the conductivity was 16.3 ± 0.1 mS · cm – 1, pH was 9.14 ± 0.01, and water temperature was 15.5 ± 0.3 ° C. These data support previous findings that S. brightwellii is a brackish diatom species.