Achnanthidium sinense, Liu & Blanco & Long & Xu & Jiang, 2016

Liu, Bing, Blanco, Saúl, Long, Hua, Xu, Jingjing & Jiang, Xiaoyan, 2016, Achnanthidium sinense sp. nov. (Bacillariophyta) from the Wuling Mountains Area, China, Phytotaxa 284 (3), pp. 194-202 : 196-198

Achnanthidium sinense Bing Liu et S. Blanco ( Figs 2–41 )

LM: Valves narrowly lanceolate with round, acute ends, 17.5–31.7 (median 28.3) μm long and 4.1–6.0 (median 5.1) μm wide (n = 50). Raphe valve possessing a narrow, lanceolate axial area, which widens slightly from the poles to the middle portion of the valve ( Figs 2–11 ). Proximal raphe ends distinct, teardrop-shaped ( Figs 2–11 ). Striae on the raphe valves not discernible except in the middle part of valve, where a few stria rows become resolvable due to a wider spacing ( Figs 2–11 ). Rapheless valve with a linear-lanceolate axial area widening slightly in the middle ( Figs 12–20 ). Striae on the rapheless valves not countable except in the middle part of valve, where a few stria rows become resolvable due to a wider spacing ( Figs 12–20 ). Frustules in girdle view shallow v-shaped ( Fig. 21 ).

SEM: Outline of raphe valve narrowly lanceolate, with a narrow lanceolate axial area and a rhombic-lanceolate central area ( Figs 22–29 ). Outline of rapheless valve also narrowly lanceolate, with a linear-lanceolate axial area and an elliptic-lanceolate central area ( Figs 30–31 ). Externally, terminal raphe fissures hooked towards the same side of the valve, central raphe endings teardrop-shaped ( Figs 22, 24–26 ). Internally, distal raphe endings terminating in small helictoglossae, proximal raphe endings curved towards opposite sides ( Figs 27–29 ). Striae slightly radiate throughout both valves except at the apices of the raphe valve, where they become parallel or slightly convergent ( Figs 22–31 ). Stria density 21–28 in 10 μm at the valve center and up to 40 in 10 μm near apices of raphe valve, 21–27 in 10 μm at the valve center and up to 34 in 10 μm near apices in the rapheless valve. Areolae external openings are small, round, or transapically elongated, whereas internal openings are transversely elliptical ( Figs 24–29 ). Each stria in the middle part of the raphe valve is composed of 1–6, usually 5–6 areolae ( Figs 22, 25 , 34–37 ). Each stria in the middle part of the rapheless valve is composed of 1–7, usually 6–7 areolae ( Figs 30 , 38–41 ). Around the central areas of both valves, the striae are more widely spaced and shortened; sometimes very short marginal striae (composed of 1–3 areolae) are present ( Figs 34–41 ). Frustules in girdle view shallow v-shaped, each valve mantle with a row of slit-like areolae and 2–3 notches ( Figs 32–33 ).

Type: — CHINA. Guizhou: Fanjing Mountain National Nature Reserve, the river course at the gate of Shengtai Zhiwu Yuan, 27° 49’ 48” N, 108° 45’ 53” E, 500 m a.s.l., Bing Liu , 31 December 2015, (holotype BM! 101841, illustrated in Figs 11, 14 ; isotype JIU! G201601 , illustrated in Figs 2, 12 ) .

Etymology: —Named after China, the country where the species was found.

Ecology: —The following environmental parameters were measured in the field. Electric conductivity was 41.9 ± 0.2 μS/cm, pH was 7.6 ± 0.1, and water temperature was 9.7 ± 0.2 °C. Since the diatom sample was scraped off the surfaces of stones and the water electric conductivity is below 50 μS/cm, Achnanthidium sinense can be considered an epilithic diatom characteristic of low electrolyte content freshwaters.

Figures

FIGURES 2–21. Achnanthidium sinense, sp. nov., LM. 2–11. Ten raphe valves showing size reduction, note the lanceolate valve outline and distinct proximal raphe ends. 12–20. Nine rapheless valves showing size reduction, note the lanceolate valve outline. 2 and 12. Photographs of isotype specimens. 11 and 14. Photographs of holotype specimens. 21. Girdle view, note the shallow v-shaped outline. Scale bar (in Fig. 2) = 10 μm for all figures.

FIGURES 22–29. Achnanthidium sinense, sp. nov., raphe valves, SEM. 22. External view of raphe valve, note the narrow lanceolate axial area. 23. Internal view of raphe valve, note the narrow lanceolate axial area. 24–26. Details of Fig. 22, note the hooked terminal raphe fissures and parallel or slightly convergent striae at the apices. 27–29. Details of Fig. 23, note the parallel or slightly convergent striae at the apices, and curved proximal raphe endings. Scale bars = 5 μm.

FIGURES 30–33. Achnanthidium sinense, sp. nov., SEM. 30. External view of rapheless valve, note the slightly radiate striae throughout the valve. 31. Internal view of rapheless valve, note the slightly radiate striae throughout the valve. 32–33. Girdle views. 32. Proliferating cells, note the notches on the mantles. 33. A frustule with convex rapheless valve discernible. Scale bars = 10 μm.

FIGURES 34–41. Achnanthidium sinense, sp. nov., SEM. 34–41. External views of middle part of raphe valve, note the stria variation around the central area. 38–41. External views of middle part of rapheless valve, note the stria variation around the central area. Scale bars = 5 μm.