Achnanthes licunese W. Chen, P. Yu & G.F. Song & R. Abate

Chen, Wei, Yu, Pan, Song, Gaofei & Abate, Rediat, 2024, A new freshwater species Achnanthes licunese sp. nov. (Achnanthaceae, Bacillariophyta) from pebbles of Licun River, Shandong Province, China, Phytotaxa 649 (1), pp. 69-82 : 71-79

Achnanthes licunese W. Chen, P. Yu & G.F. Song & R. Abate , sp. nov. ( Figs 1–40 )

LM description: Frustule usually chain-forming in colonies ( Figs 1–8 ), with concave raphid valves (RV) and convex araphid valves (ARV) ( Figs 9–20 ). Each cell possesses two chloroplasts, separated by median transapical plane. Valves linear to linear-lanceolate with obtuse apices, slightly constricted at center. Valves length 38.0–53.5 μm, width 10.0– 12.5 μm (n = 200). Single row of areolae located between transapical costae, and 9–10 striae in 10 μm on both RV and ARV. RV with stauros reaching valve margins, while longitudinal raphe sternum runs along apical axis to center of valve. ARV without stauros but with sternum, often shifted to valve margin, narrow and linear.

SEM description ( Figs 21–40 ): External RV valve face gently concave around transapical axis in girdle view, with at least three bands connecting two valves ( Fig. 21 ). 2–4 rows of areolae present on mantle, no areolae in center ( Figs 21–23 ). Band areolae similar to those on valve face. Rows of silica granules of varying sizes present at margin of valve mantle ( Figs 22–23 , wavy arrows). RV raphe filiform and straight, with proximal raphe ends straight and teardrop-shaped (Figs 24, 26), distal raphe ends deflected to same side (Figs 24–25, 27). Internally, RV with distinct stauros and costae extending from raphe sternum. Stauros robust ( Figs 28–29 ), costae more robust at margin of valve (mantle) ( Figs 28, 31 ). Central raphe fissure appears small and hooked-shaped ( Fig. 29 ); terminal fissures turn slightly in opposite direction of proximal ends, terminate in small C-shaped helictoglossae ( Fig. 31 ). External valve surfaces of ARV slight depression around valve margin ( Figs. 32–35 ). Cone-shaped spines distributed along margin on ARV ( Figs 21 , 32–33, 35 , arrows). Internally, transapical costae thickened, sternum offset from center, elevated higher than costae ( Figs 36–37 ). Areolae round or oval. Uniseriate striae composed of 2–7 areolae in middle portion of valve (Figs 24, 27), 1–7 areolae at apex (Figs 24–25, 27). On both valves, areolae occluded by complex cribra, often supported by 2–8 pegs, at almost same level with external valve surface of RV and ARV (Figs 25˗27, 33˗35). Occlusions evidently absent internally from valve surface of RV and ARV ( Figs 29–31 , arrows, 37–40). Marginal ridge and terminal orbiculi not observed.

Type: — CHINA, Shandong Province, Licun River, 36°9′24.77″N, 120°25′37.92″E, 18 m a.s.l., Wei Chen, 4 th December 2021. Slide no. HBI! LC06, holotype, retained in: Freshwater Algal Herbarium ( HBI), Institute of Hydrobiology, Chinese Academy of Science, Wuhan, China. Representative specimens on Figs 11 and 18 .

Etymology: —The species name was coined after the name of the river it was discovered, the Licun River in Shandong Province ( China).

Distribution: —The newly described species is currently known only from its type locality.

Ecology: —Water temperature was 11.9 ℃, pH was 7.3, dissolved oxygen was 11.5 mg ·L- 1, oxidation-reduction potential was 135 mv, and turbidity was 4.2 NTU. The concentrations of nitrate, nitrous, ammonia, and total phosphorus were 4.8 mg ·L- 1, 0.026 mg ·L- 1, 0.27 mg ·L- 1, and 0.17 mg ·L- 1, respectively.

Figures

FIGURES 1–2. Achnanthes licunses sp. nov. LM, the live cells 1. An unprocessed cell in girdle view. 2. Two unprocessed cells in girdle view. Scale bar: 10 μm.

FIGURES 3–20. Achnanthes licunese sp. nov. LM. 3–8. frustule in girdle view. 9–14. size diminution series of raphe valve. 15–20. size diminution series of rapheless valve. Scale bar: 10 μm.

FIGURES 21–23. Achnanthes licunese sp. nov. SEM, girdle view. 21. a complete girdle view of the frustule and the cone-shaped spines (arrows). 22–23. middle detail of 21, showing the areolae and silica granules on the girdle bands (wavy arrows). Scale bar: 10 µm (21); 2 µm (22–23).

FIGURES 28–31. Achnanthes licunese sp. nov. SEM, the internal view of raphid valve (RV). 28. internal view of the whole valve. 29. central area of the valve, showing the proximal raphe ends, and central raphe endings are hookshaped. 30. detail of the internal areolae, showing the areolae is not occluded by the complex cribra. 31. apices of the valve, showing the detail view of areolae (arrows), terminal raphe fissure, helictoglossae, and margin of valve. Scale bars: 10 µm (28); 2 µm (29); 1 µm (31); 0.5 µm (30).

FIGURES 32–35. Achnanthes licunese sp. nov. SEM, the external view of araphid valve (ARV). 32. external view of the whole valve. 34. central area of ARV. 33, 35. details of the apices of the valve, showing areolae and spines on the valve. Scale bars: 10 µm (32); 2 µm (34); 1 µm (33, 35).

FIGURES 36–40. Achnanthes licunese sp. nov. SEM, the internal view of araphid valve (ARV). 36. internal view of the whole valve. 37. central area of ARV. 38. detailed internal view of virgae and areolae 39–40. apices of ARV. Scale bars: 10 µm (36); 2 µm (37); 1 µm (38–40).