Bacillaria sinensis Bing Liu & D.M. Williams, 2021

Long, Ji-Yan, Williams, David M., Liu, Bing & Zhou, Yang-Yan, 2021, Two new freshwater species of Bacillaria (Bacillariophyta) from Dongting Lake, China, Phytotaxa 513 (3), pp. 243-256 : 245-249

Bacillaria sinensis Bing Liu & D.M. Williams sp. nov. ( Figs 1–29 )

LM: Valves linear-lanceolate, often with slightly swollen central margins (e.g. Figs 1–9 ), tapering to cuneate or rostrate apices ( Figs 1–11 ). Valve dimensions (n = 40): 52–84 μm long, 4.6–5.6 μm wide. Fibulae distinct, situated approximately along valve midline, unevenly spaced, 7–12 in 10 μm. Striae indistinct, parallel throughout valve, 27–29 in 10 μm. Fault sites on valve broader side difficult to discern using LM.

SEM: Colony and frustule view: Cell to cell attachment forms colony ( Figs 12, 13 ). Frustule composed of (probably) five open girdle bands ( Figs 14–17 , labeled B1 to B5), four associated with the epivalve, only one is seen with the hypovalve ( Figs 16, 17 ). Pars exterior deeper than pars interior, stepped, two rows of poroids located in pars exterior along midline, except near each apex becoming one row ( Figs 15, 16 , arrow, 17). Poroids of valvocopula covered externally by hymenes ( Figs 15–17 ).

Valve view: Valve linear-lanceolate, with slightly swollen central margins ( Figs 18 , 24 ). Raphe nearly central, continuous from pole to pole, distal raphe endings T-shaped (‘tongue-in-groove’ structure); two raphe flanges present on each side of raphe, asymmetrical due to raphe flange on narrower valve side more developed than that on broader side, terminating before reaching poles ( Figs 14–23 ). Transapical ribs originate with raphe ribs, parallel; striae uniseriate, composed of rounded areolae covered by hymenes externally, continuing onto mantle. Marginal spines absent. On broader side of valve, one transapical rib forming two branches at some sites ( Figs 19, 21 , 25, 28, 29 , arrow, respectively), or two merging into one occasionally ( Figs 15 , curved arrow; 19, 22, 23, 29, three curved arrows, respectively). Fibulae rib-like, arching into cell ( Figs 24–29 ). Two fibular ribs asymmetrical, i.e. fibular rib on broader side of valve more developed than that on narrower side ( Fig. 26 , arrows). Internally, raphe straight, continuing from pole to pole where its distal raphe fissure curves into raised helictoglossa ( Figs 26, 27 ).

Type:— CHINA. Hunan province: West Dongting Lake, Yang’s Village, a sampling point near the lakeshore, 28° 52’ 29.5” N, 112° 16’ 52” E, 50 m asl., Bing Liu , 23 rd April 2017 (holotype BM! 81944, specimen circled on slide, illustrated as Fig. 1 ; isotype JIU! G202101 , specimen circled on slide, illustrated as Fig. 3 ) .

Etymology:—Named after China where the species was found (the specific locality is Dongting Lake).

Ecology:— Bacillaria sinensis was commonly found in the surface sediment collected in West Dongting Lake. Associated species comprised Entomoneis triundulata Bing Liu & D.M. Williams (in Liu et al. 2018: 242), Ulnaria dongtingensis Bing Liu (in Liu et al. 2019: 127), and some species of Navicula Bory (1822: 128) , Nitzschia Hassall (1845: 435) , Sellaphora Mereschkowsky (1902:186) , Surirella Turpin (1828: 362 , 363), Tryblionella Smith (1853: 35) , and others. The following environmental parameters were measured in the field. Conductivity was 109.3 ± 0.1 μS∙ cm-1, pH was 8.3 ± 0.2 and water temperature was 23.5 ± 0.3 °C. Since the diatom sample was collected using lens tissue from the mud surface and the water conductivity is above 100 μS∙ cm-1, Bacillaria sinensis can be considered an epipelic alkaliphilous diatom characteristic of moderate electrolyte content in freshwaters.

Figures

FIGURES 1–11. Bacillaria sinensis sp. nov., LM. 1–11. Eleven valves showing size diminution series, note that valves are often slightly swollen in the middle (e.g. Figs 1–8). Fig.1. Micrograph of holotype specimen. Fig. 3. Micrograph of isotype specimen. Scale bar = 10 μm.

FIGURES 12–17. Bacillaria sinensis sp. nov., colony and frustule view, SEM. 12. A collapsed colony. 13. Apical detail of Fig. 12. 14. A dismantled frustule. 15. Middle detail of Fig. 14, note two asymmetrical raphe flanges (RF), two transapical ribs merging into one and one shorter stria (curved arrow), and valvocopula. 16. An apical detail of Fig. 14, showing five girdle bands (B1 to B5) and two rows of poroids along the midline of valvocopula (arrow). 17. Another apical detail of Fig. 14, showing two asymmetrical raphe flanges (RF) and five girdle bands (B1 to B5). Scale bar =10 μm (Figs 12, 14), 5 μm (Figs 13, 16), 1 μm (15, 17).

FIGURES 18–23. Bacillaria sinensis sp. nov., external view, SEM. 18.A complete valve. 19. Middle detail of Fig. 18, note one transapical rib forming two branches (arrow) and two transapical ribs merging into one (three curved arrows). 20.An apical detail of Fig. 18, showing two asymmetrical raphe flanges (RF) and T-shaped distal raphe end. 21. Another apical detail of Fig. 18, note one transapical rib forming two branches (arrow). 22. Middle part of Fig. 18, note two transapical ribs merging into one (three curved arrows). 23. Other valve apex, showing two transapical ribs merging into one (three curved arrows). Scale bar = 10 μm (Fig. 18), 2 μm (Figs 19–23).

FIGURES 24–29. Bacillaria sinensis sp. nov., internal view, SEM. 24.A complete valve. 25. Middle detail of Fig. 24, note one transapical rib forming two branches (arrow) and fibulae (F). 26. An apical detail of Fig. 24, note two asymmetrical fibular ribs. 27. Another apical detail of Fig. 24, note one transapical rib forming two branches (arrow). 28. Other valve middle part, note one transapical ribs forming two branches (arrow). 29. Other valve apex, note one transapical ribs forming two branches (arrow) and two transapical ribs merging into one (three curved arrows). Scale bar = 10 μm (Fig. 24), 2 μm (Figs 25–29).