Encyonema chebalingense W.Zhang & S.Blanco, 2021

Huang, Ruohan, Ma, Jin, Wang, Xianyun, Blanco, Saúl, Kociolek, John Patrick & Zhang, Wei, 2021, Encyonema chebalingense sp. nov., a new freshwater diatom species (Cymbellales, Bacillariophyceae) from Guangdong Province, China, Phytotaxa 508 (1), pp. 77-84 : 78-79

Encyonema chebalingense W.Zhang & S.Blanco sp. nov. Figs 1–21

Description:—LM: Valves distinctly asymmetrical and dorsiventral, semielliptical or semielliptical-lanceolate, dorsal margin clearly arched, ventral margin nearly straight or slightly concave. Both ends gradually narrowed, apices not or only slightly protracted, broadly to obtusely rounded ( Figs 1–9 ). Length of the observed specimens 17.8–26.0 μm, width 5.2–6.7 μm, length/width ratio 3.4–3.9 (n=17). Raphe slightly inclined to the ventral margin, nearly straight and linear. The proximal raphe end is slightly curved to the dorsal margin, the end slit of the distal end is close to the valve edge and conspicuously curved to the ventral margin. Axial area narrow, conspicuously inclined to the ventral side, and one stria (sometimes two) on the middle ventral side is shorter. Striae radiate with areolae indistinguishable under LM. Terminal striae density 10–11 in 10 μm, becoming 8–10 in 10 μm toward the central area.

SEM: Externally, the valve of E. chebalingense is flat and the transition from the valve face to the mantle is gradual ( Figs 10, 11 ). No stigmoids are present in the central area ( Figs 12, 13 ). The proximal ends of the raphe are clearly enlarged and inclined to the dorsal side, while terminal fissures are hooked to the ventral side of the valve at an angle of almost 90°. The axial area is narrow and linear ( Figs 10, 11, 14, 15 ). Most of the striae are composed by single areolae of different sizes and shapes, mostly short lineolae or slit-like. The middle part of the ventral side has significantly shortened striae ( Figs 10–13 ). Internally, the proximal raphe endings are hidden by an overgrowth of silica ( Fig.18 ), distal raphe ends terminate in small helictoglossae ( Figs 16, 17, 19–21 ). The uniseriate areolae of each stria are arranged between the interstria, and short tectullae project within the striae ( Figs 16–20 ). Areolae 40–45 in 10 μm within ventral and dorsal striae.

Type:— CHINA. Guangdong Province: Shixing County, Shaoguan City, upper reaches of Mojiang River , 24°43’21” N, 114°15’24” E. 357 m asl, Date: X.L. Lin August 23 2020 .

Etymology:—The specific epithet “ chebalingense ” refers to the place from which this new species was collected.

Figures

FIGURES 1–9. Encyonema chebalingense sp. nov. LM. Size diminution series of individuals from the holotype slide. Valve views. Scale bar =10 μm

FIGURES 10–15. Encyonema chebalingense sp. nov. SEM images from type material. External views. 10–11. Valve in external view. 12–13. Apex of valve showing proximal raphe endings. 14. External view of the valve center. Note the distal raphe endings ae hooked towards the ventral margin. 15. Distal raphe ending at valve apex. Scale bars = 1 μm (12), 1.5 μm (15), 2 μm (13, 14), 2.5 μm (11), 5 μm (10).

FIGURES 16–21. Encyonema chebalingense sp. nov. SEM images from type material, internal views. 16. Entire valve view. 17–21.Apex of valve with distal raphe ending terminating as a helictoglossa. Fig. 18. Valve center showing central nodule with proximal ends of the raphe hidden by siliceous covering. Figs 19–21. Distal raphe end showing helictoglossa. Scale bars = 1 μm (19–21), 2 μm (Fig.17–21): 2.5 μm (16).