Cymbella erhaiensis Y.-L. Li, 2025

Zheng, Kun, Xiao, Qiao-Zhi, Guo, Ji-Shu, Huang, Ji-Min, Zhang, Yun, Kociolek, John Patrick & Li, Yan-Ling, 2025, Cymbella erhaiensis sp. nov., a new cymbelloid diatom species (Cymbellales, Bacillariophyta) from Yunnan Province, China, Phytotaxa 683 (2), pp. 145-155 : 146-147

Cymbella erhaiensis Y.-L. Li , sp. nov. ( Figs 1 –14)

Description:— LM ( Figs 1–5 ): Valve strongly dorsiventral, asymmetrical about the apical axis, symmetrical about the transapical axis. Dorsal margin strongly arched, ventral margin slightly concave but with slightly tumid central part. Valve ends narrowly rounded, not protracted. Length 56.0–77.5 µm, width 16.0–20.5 µm, length/width ratio between 3.4–3.8, median 3.6 (n = 10). Axial area lanceolate, gradually narrow towards both ends. Central area linear to lanceolate, about 1/4–1/3 the width of the valve. Raphe lateral, becoming filiform near the distal and the proximal ends. Striae radiate towards the poles, density 9–11 in 10 μm in the middle portion, up to 13–14 in 10 μm toward the ends. Areolae visible, 14–16 in 10 μm. Stigma absent.

SEM: Valve exterior ( Figs 6–9 ): Valve face flat, axial area thickened ( Figs 6 , arrow A). Externally, raphe displaced dorsally, slightly curved ventrally near the valve center and with drop-like central pores at the proximal raphe ends, distal raphe end fissures hooked and deflected towards the dorsal margin ( Figs 6–8 , arrow B). Each valve apex has an apical pore field, comprised of small, round porelli that are physically separated and morphologically distinct from the areolae. The distal raphe ends extend onto the mantle but do not bisect the apical pore fields ( Figs 8–9 ). Striae uniseriate. Areolae mostly with C-shaped openings with T-shaped occlusions, other openings S-shaped or slit-like ( Fig 9 , arrows C, D, E). Stigma absent.

Valve interior ( Figs 10–13 ): Striae uniseriate, internal areolae with mostly C-shaped openings ( Fig 10 ). Internal raphe continuous, without intermissio, and central area with distinct central nodule ( Fig 11 , arrow F), each end of the raphe terminates distally with a small, knob-like helictoglossa slightly offset from the main raphe branch towards the dorsal margin ( Figs 10, 12 ). Porelli of the apical pore fields internally occluded ( Fig 13 , arrow G). Stigma absent.

Type: — CHINA. Yunnan Province: Dali Bai Autonomous Prefecture, Erhai Lake , elevation 1972 m a.s.l., 25.6054°N, 100.23123°E, EH1–8 , sample collected by Dr. Yun Zhang, 7 January 2022. (Holotype EH 2022010708 in Coll.Yan-Ling Li, Yunnan University, Kunming, China = Fig. 1 ; Isotype YUNGL20220331 , Harbin Normal University, Harbin, China) .

Etymology: —The specific epithet ‘ erhaiensis ’ refers to the locality from which the new species was collected.

Ecology: — Cymbella erhaiensis sp. nov. has been observed on epilithic samples from Lake Erhai, a habitat with mesotrophic level (TN 541 μg/L, TP 23 μg/L), weakly alkaline habitats (pH 8.31) and low conductivity (230 μS/ cm). This species was mainly associated with Nitzschia palea var. debilis (Kützing) Grunow (1880: 96) (35.7 %), Gomphonema insigne W. Gregory (1856: 12) (12.7 %), Nitzschia dissipata (Kützing) Rabenhorst (1860: no. 968) (11.2 %), Gomphonema sp (10 %), Nitzschia dealpina Lange-Bertalot & G. Hofmann (1993: 146) (4.7 %), Diatoma vulgaris Bory (1824: 461) (4.5 %), Fragilaria recapitellata Lange-Bertalot & Metzeltin (2009: 48) (2 %), and the new species is about 1.6 %.

Figures

FIGURES 1–5. Cymbella erhaiensis sp. nov., LM, DIC. Valve views, showing size range and variability of the holotype population. Scale bar = 10 μm.

FIGURES 6–9. Cymbella erhaiensis sp. nov., SEM, external views. Fig. 6. External view of the entire valve, arrow A indicates the axial area thickened. Fig. 7. External view of valve centre showing the proximal raphe endings. Fig. 8. Detail of valve showing the distal raphe ends curved towards the dorsal margin (arrow B). Fig. 9. Detail of valve apices showing apical pore field with small and round porelli, arrows C, D and E indicate C-shaped, S-shaped and slit-like of the areolae, respectively. Scale bar = 3 μm (Fig. 6), 2 μm (Fig. 7–9).

FIGURES 10–13. Cymbella erhaiensis sp. nov., SEM, internal views. Fig. 10. Internal view of entire valve. Fig. 11. Detail of the valve central area showing the intermissio is lacking with the central nodule and no stigma present, arrow F indicates the central nodule. Figs 12, 13. Detail of valve ends with small, knob-like helictoglossa slightly deflected to the dorsal side, arrow G indicates the apical pore field with porelli internally occluded. Scale bars = 2 μm.