Gomphocymbellopsis guijiangensis Y. -L. Li 2023

Gomphocymbellopsis guijiangensis Y.-L. Li, sp. nov.

(Figs 1–17)

Description: LM (Figs 1–8): Valves lanceolate with broadly rounded apices, slightly dorsiventral and heteropolar, commonly asymmetrical about the apical axis with a moderately inflated central portion gradually tapering to the head pole and foot pole. Dorsal and ventral margins similarly arched. Valve length 30.0–36.0 μm, valve width 8.0–13.5 μm, valve length/width ratio varying between 2.6–4.3, median 3.5 (n = 30). Raphe slightly lateral, occasionally appearing slightly reverse-lateral near the central ends, narrowing and becoming filiform towards the distal ends. External central raphe ends deflected gently towards the ventral side, appearing as slightly inflated central pores. External terminal raphe fissures hooked and deflected towards dorsal margin. Axial area very narrow, moderately curved, not or slightly expanded proximally, approximately in the median line of the valve. Central area lacking or not well defined, with one markedly shortened stria near the valve centre. Striae nearly parallel around the valve centre, becoming slightly radiate towards the poles, indistinctly punctate, more widely spaced near the markedly shortened stria, density 7–9 in 10 µm in the middle portion, up to 8–11 in 10 µm towards the ends. Individual areolae not visible.

SEM: Valve exterior (Figs 9–13): Striae biseriate, occasionally uniseriate adjacent to the axial area, almost parallel in the middle, slightly radiate towards both ends (Figs 9–13). Areolae round to elliptical, 60–80 in 10 μm (Figs 10–13). Apical pore fields present at head pole and foot pole on the mantle, entire (not bisected) and clearly physically separated and morphologically distinct from the areolae (Figs 9–12). Three external, round to elliptical stigma openings present on the ventral side (Figs 10, 13).

Valve interior (Figs 14–17): Striae formed by biseriate, rounded-elliptical areolae delimited by slightly oblique orientated vimines (Figs 14–17). The internal raphe slit continuous, without an intermissio (Figs 14, 17). Terminal raphe ends offset, bent slightly towards the dorsal margin, and terminating in small, knob-like helictoglossae adjacent to the shortened striae (Figs 14–16). Three internal, elliptical or slit-like stigma openings present on the ventral side (Figs 14, 17).

Type:— CHINA. Guangxi Province: Guijiang River, freshwater, 24°15′23.89478″ N, 110°46′2.05771″ E, elevation 97.495 m a.s.l., 1st July 2021, rock scraping samples collected by Prof. Yan-Ling Li (Holotype GJ 2021070101 in Coll. Yan-Ling Li, Yunnan University, Kunming, China = Fig. 1; Isotype YUNGL20220120, Harbin Normal University, Harbin, China).

Etymology:— guijiangensis, referring to the type locality from which the new species was obtained.

Ecology: — Gomphocymbellopsis guijiangensis was found in a low altitude freshwater lake with moderately alkaline pH (8.35), dissolved oxygen of 7.94 mg /L, and conductivity of 181.5 μS/cm.At the type locality G. guijiangensis was uncommon (<1% abundance); the related species in decreasing order of abundance were Achnanthidium biasolettianum (Grunow) Lange-Bertalot (1999) (74.7 %), Cymbella turgidula Grunow (in Schmidt 1875: 9) (8.2 %), Navicula cryptotenella Lange-Bertalot (Krammer & Lange-Bertalot 1985: 43) (7.4 %), Nitzschia palea (Kützing) W. Smith (1856: 89) (4.0 %), Gomphonema pumilum (Grunow) E. Reichardt & Lange-Bertalot (1991: 528) (1.6 %), G. minutiforme Lange-Bertalot & E. Reichardt (1993: 61) (0.8 %), Aulacoseira granulata (Ehrenberg) Simonsen (1979: 58) (0.5 %), C. tumida (Brébisson) Van Heurck (1880: 64) (0.5 %), Fragilaria tenera (W. Smith) Lange-Bertalot (1980: 746) (0.5 %), F. capucina Desmazières (1830: 453) (0.4 %), Planothidium lanceolata (Brébisson ex Kützing) Lange-Bertalot (1999: 287) (0.3 %), G. parvulum (Kützing) Kützing (1849: 65) (0.3 %), Synedra ulna (Nitzsch) Ehrenberg (1832: 87) (0.3 %), Psammothidium curtissimum (Carter) Aboal (Aboal et al. 2003) (0.1 %), and one unidentified species of Sellaphora C. Mereschkowsky (1902).

A second species was found in sediments of the Jianghan Plain (Figs 18–25) that is a putative additional new species of Gomphocymbellopsis. Specimens of this species have only been observed with LM to date. Specimens are 16.5–25.5 µm long and 4.5–6.0 µm wide. They have a length/width ratio that varies between 3.4–5.3, with a median of 4.6. The raphe is lateral and slightly undulate. The axial area is narrow, becoming laterally expanded at the rectangular central area. Striae are radiate, becoming parallel at the apices. Stria density 8–14 in 10 µm in the center of the valves, up to 9–13 in 10 µm towards the ends. No stigmata have been observed. These specimens appear similar in general overall construction of G. guijiangensis but SEM observations are needed to confirm its systematic placement.