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).