Gomphonema rajaguruii M.Yogeshwaran, Kociolek & B.Karthick, sp. nov. (Figs 1–30)

Description:— LM (Figs 1–12): Valves heteropolar, lanceolate to rhombic, slightly broad rounded head pole, rounded narrow foot pole, length 45.5–71.0 μm, breadth 9.0–13.0 μm (n = 64).Axial area slightly broader and linear to lanceolate. Central area distinct, circular, formed by short striae, transapically elongated isolated stigma present. Raphe lateral, weakly undulate, with proximal ends dilated and distal ends curved onto the valve mantle. Striae 8–10 in 10 µm in the middle of the valve, 10–12 in 10 µm at poles. Striae parallel at the head pole, slightly radiate near center, becoming radiate at the foot pole. Areolae not visible in LM. Apical pore field (APF) prominent at foot pole.

SEM external valve views (Figs 13–20): Externally, valves lanceolate to rhombic in shape (Figs 13, 14), biseriate slit-shaped areolae (Fig. 15), arranged alternately, non-parallel, unorganised directions. Areolae 60–70 in 10 μm, 300–360 nm in size, comprise the striae and extend onto the valve mantle (Fig. 16). On the mantle, a series (4–5) of solitary pores present (Fig. 20, arrow). Raphe weakly undulate (Fig. 14). Distal raphe ends deflected onto valve mantle before the apices towards the same side (Fig. 17). Proximal raphe ends dilated, teardrop-shaped and deflected towards isolated oval stigma in the central area (Fig. 18). At the foot pole, the raphe bisects the bilobed apical pore field (Figs 19, 20). APF separated from striae by a hyaline area. Apical pore field porelli morphologically distinct from areolae.

SEM internal valve views (Figs 21–30): Internally, striae slightly radiate at center, strongly radiate at foot pole, almost parallel at head pole (Fig. 21). Distal raphe end terminates before valve apices as prominent helictoglossae (Fig. 22–25). Proximal raphe ends angular, hooked deflected towards stigma opening side (Fig. 26). Slit-like stigma opening at central nodule (Fig. 26, arrow). Rounded areolae alternately arranged (Fig. 27) with c-shaped flaps evident (arrow). Pseudoseptum present at both apices (Figs 22–25). Apical pore field internally covered under pseudoseptum (Fig. 25, arrow). The presence of thick costae underneath the margin and the mantle shows marginal lamina is present (Figs 28–30). On the marginal lamina, a series (3–4) of solitary pores present (Fig. 29, arrow).

Type:— INDIA, Maharashtra, composite biofilm collection on a roadside wet wall at Mahabaleshwar (17°55’42.85” N, 73°37’57.40” E; elevation 957 m asl), Dec. 10 2013, (holotype (here designated): #123, slide #02–046 AHMA = Fig. 7).

Etymology:— The species is named after Prof Sharad Narhar Rajaguru (1933–2022), Indian geoarchaeologist and Quaternary geologist from Deccan College, Pune, Maharashtra, India, who passed away recently on December 15, 2022. He contributed to the Quaternary research across mainland western India, evolution of the Deccan Volcanic Province, and the formation of laterite plateaus of the WG.

Ecology:— The new species grows on a wet wall. The collection site had a water temperature of 20.6 °C, neutral pH of 6.9 and low EC (39.5 μs/ cm−1). DO was 8.3 ppm; the nitrate and phosphate of the water collected at waterfalls were 1.6 ppm and 0.33 ppm, respectively. The new species was dominant in the sample. It was accompanied by undescribed species belonging to the genera Navicula J.B.M. Bory de Saint-Vincent (1822: 128), Cymbella C.A. Agardh (1830: 1), and Ulnaria (Kützing) P. Compère (2001: 100).