Oricymba gongshanensis, Guo & Meng & He & Zhang & Li & Kociolek, 2021

Guo, Ji-Shu, Meng, Wen-Wen, He, Xiao-Yang, Zhang, Yun, Li, Yan-Ling & Kociolek, John Patrick, 2021, Oricymba gongshanensis sp. nov. (Cymbellaceae; Bacillariophyceae), a new species from southwest China, Phytotaxa 508 (1), pp. 39-48 : 45

Oricymba gongshanensis J.-S. Guo & Y.-L. Li, sp. nov. (Figs 1–19)

LM (Figs 1–9): Valves linear-lanceolate, nearly symmetrical to slightly asymmetrical about the apical axis, with a moderately inflated central portion gradually tapering or nearly parallel to bluntly-cuneate poles. Length 46.5–64.5 μm, width 10.5–12.3 μm, length/width ratio 4.4–5.2, median 5.0 (n = 30). Raphe filiform near the central area, becoming lateral, with external raphe fissures somewhat undulate, internal raphe fissures straight. External proximal raphe ends expanded, deflected towards the ventral side. External distal raphe fissures hooked towards dorsal margin. Axial area lanceolate. Central area rhombic-lanceolate, extremely asymmetrical, occupying nearly 1/3 of the valve width, with 1–4 slightly shortened central dorsal striae, 3–8 markedly shortened central ventral striae. Distinct isolated stigma lies between the protruding central nodule and the two central striae on the ventral side. Striae biseriate, with dorsal striae almost parallel at the valve centre, becoming slightly radiate towards the poles, ventral striae slightly radiate throughout, 7–11 in 10 μm. Areolae visible, 66–100 in 10 μm.

SEM: Valve exterior (Figs 10–16): raphe undulate with proximal raphe ends slightly dilated, weakly bent ventrally (Figs 15, 16), distal fissures hooked, deflected towards the dorsal side (Figs 12–14). Striae biseriate, occasionally uniseriate adjacent to the axial area (Figs 12–15). Areolae mostly rounded or elliptical, occasionally elongate rectangular openings (Figs 12–16). Areolae may contain small occlusions (Fig. 16). Longitudinal ridges are very thick along the valve margins except near the valve terminus with distinct and shallow grooves along both the valve face and mantle edges (Figs 10, 11). Apical pore fields present at both ends on the mantle and clearly physically separated and morphologically distinct from the areolae (Figs 12–14).

Valve interior (Figs 17–19): striae formed by rounded-elliptical, biseriate, occasionally elongate areolae separated by robust silica ribs (Figs 17–19). The internal raphe continuous without intermissio (Figs 17, 19), distal raphe ends offset, bent slightly towards the dorsal margin, and terminate in small, knob-like helictoglossae (Fig. 18). Two internal, narrow, slit-like stigma openings on the ventral side occluded by fine ingrowths from the perimeter (Fig. 19). The dentate occlusions of areolae are evident from the interior (Figs 17–19).

Type:— CHINA. Yunnan Province: Gongshan country, Gaoligong Mountain , GS 1, 27°46′44″ N, 98°27′49″ E, elevation 3200 m a.s.l., samples collected by Prof. Yan-Ling Li, 9 August 2019. Holotype GS 2019080901 in Coll. Yan-Ling Li, Yunnan University, Kunming, China. Figure 1 is of the holotype.

Etymology: — gongshanensis , referring to the type locality from which the new species was described.

Ecology:— Oricymba gongshanensis is known only from a stone wall, situated at 3200 m a.s.l. This species was associated with Achnanthidium minutissimum (Kützing) Czarnecki ( Czarnecki 1994: 157) , Staurosira venter (Ehrenberg) Cleve & Möller (1877: 242), Gomphonema gracile Ehrenberg (1838: 217), Oricymba xianjuensis W. Zhang & Kociolek (2016: 135) , Encyonema minutum (Hilse) Mann (in Round et al. 1990: 167), and several at present unidentified species of Fragilaria Lyngbye (1819: 182) , Cymbella, Gomphonema Ehrenberg (1832: 87) and Encyonema Kützing (1833: 589) .