Stauroneis lacusvulcani Rioual, 2013

Rioual, Patrick, Gao, Qiang, Peng, Yumei & Chu, Guoqiang, 2013, Stauroneis lacusvulcani sp. nov. (Bacillariophyceae), a new diatom from volcanic lakes in northeastern China, Phytotaxa 148 (1), pp. 47-56 : 49-52

Stauroneis lacusvulcani Rioual sp. nov. ( Figs 2–21 )

Type:— CHINA: Inner Mongolia, Great Xing’An Mountains, Sifangshan Tianchi , 869 m, 49º 22'33''N, 123º 27'51''E, April-2008, surface sediment collected by Dr Guoqiang Chu, IGG-CAS , Beijing. (holotype slide IGGDC-DB-SIFA- 1204!, holotype specimen illustrated in Fig 7 , located using England Finder K 45/1); BM 101 674 (isotype slide) .

LM ( Figs 2–15 ): Valves lanceolate with long protracted capitate apices ( Figs 2–15 ); length 62–83 µm, width 9.2–12.0 µ m. Raphe moderately lateral, becoming filiform at distal ends, with strongly unilaterally deflected (hooked) distal ends. Axial area narrow, linear. Shape of central area varies from narrow rectangular ( Figs 2– 3, 5–6, 10–13 ) to asymmetrical stauros expanding towards valve margins ( Figs 1 , 4, 7–9, 14–15 ). Shortened striae may be present at valve margins ( Figs 2, 5–8, 9–12 ) or not ( Figs 3–4, 13–15 ). Striae parallel along border of stauros becoming radiate to more steeply radiate near valve apices, 21–28 in 10 µm.

SEM ( Figs 16–21 ): Areolae round to transapically oblong, irregularly spaced, 18–28 in 10 µm. Weakly developed hyaline area present, thus striae next to stauros appear discontinuous ( Figs 17, 20 ). Raphe bordered by wide sternum on each side. Proximal raphe ends straight and slightly expanded ( Fig. 17 ), apical external raphe endings hooked with hooks opening toward secondary side ( Fig. 18 ). Internally, raphe-sternum bears longitudinal ribs and well-developed helictoglossae ( Fig. 21 ).

Etymology:—Based on its occurrence in volcanic lakes.

Distribution and ecology:— Stauroneis lacusvulcani was found in the surface sediment of two volcanic lakes of NE China, Sifangshan Tianchi and Lake Xiaolongwan. Lake Xiaolongwan located in the Long Gang volcanic field in Jilin Province, is a small maar lake (i.e. formed by a phreatomagmatic eruption) with a maximum water depth of 15 m ( Chu et al. 2009). Sifangshan Tianchi, located in the Great Xing’An Mountains (Inner Mongolia) is a much smaller water body as only a small pond, less than 1 m deep, persists at the center of the crater. In both sites, the water is slightly acidic with low electrical conductivity and relatively high dissolved organic carbon concentration ( Table 1). For Sifangshan, however, the values for total phosphorus (TP), total nitrogen (TN) and dissolved silica were measured on a water sample that was contaminated with sediment.

In both surface-sediment samples, S. lacusvulcani is rare and represents less than 1% of the assemblages. In the sediment core from Lake Xiaolongwan, S. lacusvulcani is most abundant (14.4%) in the sample taken at 400 cm core depth from the early part of the Holocene.

Figures

FIGURE 1: Geographical location of the study sites. Lake Xiaolongwan is marked by an X, Sifangshan Tianchi by a S. Shaded areas represent mountainous regions with an elevation>1000 m.

FIGURES 2–15. Light micro-photographs of Stauroneis lacusvulcani. Scale bar = 10 µm. Figs 3,4,7,8. Specimen from Sifangshan Tianchi, surface-sediment. Figs 2, 5, 6. Specimens from Xialongwan surface-sediment. Figs 9–15. Specimens from Xiaolongwan core sample.

FIGURES 16–21. SEM of Stauroneis lacusvulcani from Sifangshan. 16. Exterior view of whole valve. 17. Close-up of valve centre. 18. Close-up of distal end. 19. Interior view of whole valve. 20. Interior view of centre showing ridge bearing raphe fissure. 21. Interior view of distal end showing helictoglossa.