Achnanthidium qingxiense Q. M. You, P. Yu & Q. X. Wang, 2022

Yu, Pan, You, Qingmin, Pang, Wanting & Wang, Quanxi, 2022, Two new freshwater species of the genus Achnanthidium (Bacillariophyta, Achnanthidiaceae) from Qingxi River, China, PhytoKeys 192, pp. 11-28 : 11

Achnanthidium qingxiense Q. M. You, P. Yu & Q. X. Wang sp. nov.

Figs 1AE -AS , 6 -9

Description.

LM (Fig. 1AE - AS ). Valves linear-lanceolate in shape, with rounded or weakly protracted apices. The valve length is 22.5-28 µm and breadth of 3.8-4.6 µm (n = 30). Raphe valve with a narrow, linear-lanceolate axial area is weakly expanded at the middle portion of the valve. Striae slightly radiate at the centre area, becoming denser towards the apices, 21-25 in 10 µm at the centre, 42-44 in 10 µm near the apices. Rapheless valve with narrow, linear axial area is weakly expanded at the middle portion of the valve. Striae are nearly parallel, becoming denser towards the apices, 20-24 in 10 µm at the centre, up to 32-34 in 10 µm at the apices.

In the SEM, on both valves, the valve mantle has a single row of slit-like areolae (Figs 6B, C , 8A, B ). Externally, the raphe is filiform, slightly undulate and has distal raphe ends deflected to the same side (Fig. 6A ). On the side of the deflection, there is a depression near the distal raphe ends (Fig. 6A, B ). The proximal raphe ends are straight and teardrop-shaped (Fig. 6A, C ). Areolae are small, round to transapically orientated, the uniseriate striae are composed of 5-8 areolae in the middle portion of the valve (Fig. 6A, C ) and 1-5 areolae at the apex (Fig. 6A, B ). Internally, distal raphe ends terminate in raised helictoglossae (Fig. 7A-C ), while the proximal raphe ends are weakly deflected in opposite directions (Fig. 7A, B, E ). Areolae transapically elongated in the central portion of the valve and becoming larger and oblong at the apices (Fig. 7A-C, E ).

Rapheless valve: Externally, the axial area is linear, being weakly expanded at the central area and distinctly expanded at the apices (Fig. 8A-E ). Striae are uniseriate, comprise of 5-10 round or transapically orientated areolae in the central area (Fig. 8A, B, E ) and 1-4 round, oblong or slit-like areolae at the apices (Fig. 8A-D ). Internally, the axial area is slightly raised, with a subtriangular area at the ends of the axial area (Fig. 9A-D ). Areolae are transapically oval in the centre of the valve (Fig. 9A, B, E ) and large, irregular and oblong at the ends (Fig. 9A-D ). On both interiors of both valves, areolae are occluded by hymenes perforated by delicate slits and each hymene joins with the adjacent hymene (Figs 7D , 9F ).

Holotype

(designated here). SHTU! Slide QXH201801-Z7 in Lab of Algae and Environment, College of Life Sciences, Shanghai Normal University, Shanghai, China. Holotype illustrated in Fig. 1AJ , AO .

Registration.

http://phycobank.org/103058

Type locality.

China. Qingxi River, Anhui Province, 30°14'39"N, 117°49'58"E, leg. Q.X. Wang and P. Yu, 23th January 2018.

Etymology.

The species is named after Qingxi River, where it was discovered.

Ecology.

Collected in one sample (QXH201801-Z7) on stone. The environmental conditions are exactly the same as for the A. dubium sp. nov.

Distribution.

The new species is known only from the type locality.

Figures

Figures 1. A-AD LM valve views of Achnanthidium anhuense sp. nov. AE-AS LM valve views of Achnanthidium qingxiense sp. nov. Scale bar: 10 µm.

Figures 6. A-C Achnanthidium qingxiense sp. nov., SEM external views of raphe valve A external view of an entire raphe valve B apices of the valve, showing the distal raphe ends C central area of the valve, showing the proximal raphe ends. Scale bars: 5 µm (A); 1 µm (B, C).

Figures 7. A-E Achnanthidium qingxiense sp. nov., SEM internal views of raphe valve A, B internal view of an entire raphe valve C apices of the valve, showing the distal raphe ends E central area of the valve, showing the proximal raphe ends D internal areola openings with fine hymenate structures. Scale bars 5 µm (A, B); 1 µm (C, E); 0.3 µm (D).

Figures 8. A-E Achnanthidium qingxiense sp. nov., SEM external views of rapheless valve A, B external view of an entire rapheless valve C, D apices of the valve E central area of the valve. Scale bars: 5 µm (A, B); 1 µm (E); 0.5 µm (C, D).

Figures 9. A-F Achnanthidium qingxiense sp. nov., SEM internal views of rapheless valve A, B internal view of an entire rapheless valve C, D apices of the valve E central area of the valve F internal areola openings with fine hymenate structures. Scale bars: 5 µm (A, B); 1 µm (E); 0.5 µm (C, D); 0.3 µm (F).