Bacillaria dongtingensis 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 : 249-254

Bacillaria dongtingensis Bing Liu & D.M. Williams sp. nov. ( Figs 30–58 )

LM: Valves linear-lanceolate, tapering to cuneate or rostrate ( Figs 30–40 ). Valve dimensions (n = 81): 53–99 μm long, 4.4–5.7 μm wide. Fibulae distinct, placed approximately along valve midline, unevenly spaced, 6–12 in 10 μm. Striae indistinct, parallel throughout valve, 24–26 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 ( Fig. 41 ). At least two open girdle bands ( Figs 43–46 , labeled B1 to B2). Poroids of valvocopula covered externally by hymenes ( Figs 45, 46 ).

TABLE 1. Comparison among similar Bacillaria species.

Valve view: Valve linear-lanceolate ( Figs 41, 43 , 47 , 53 ). Raphe nearly central, continuous from pole to pole, distal raphe endings T-shaped ( Figs 45, 46 , 49, 52 ); one raphe flange present on narrower side of valve, irregular or complete lacking, terminating before reaching poles ( Figs 42–52 , RF). Transapical ribs originated with raphe ribs, parallel; striae uniseriate, composed of rounded areolae covered by hymenes externally, continuing onto mantle. Marginal spines distinct (e.g., Figs 44–46 , 48, 49 ). On broader side of valve, transapical rib forms two branches at some sites ( Figs 42 , 50, 51, 52 , 55, 57 , arrow, respectively; 58, two arrows), sometimes two transapical ribs merge into one ( Figs 42 , 48, 50 , 54, 55 , three curved arrows, respectively). Fibulae rib-like, arching into cell ( Figs 53–58 ). Two fibular ribs asymmetrical, i.e. fibular rib on broader side of valve more developed than that on narrower side ( Figs 54, 56 , FR). Internally, raphe straight, continuing from pole to pole where its distal raphe fissure curves into raised helictoglossa ( Figs 55, 56 ).

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! 81955, specimen circled on slide, illustrated as = Fig. 30 ; isotype JIU! G202102 , specimen circled on slide, illustrated as Fig. 32 ) .

Etymology:—Named after Dongting Lake, where the species was found.

Ecology:— Bacillaria dongtingensis was commonly found in the surface sediment collected in West Dongting Lake with B. sinensis . For details see above.

Figures

FIGURES 30–40. Bacillaria dongtingensis sp. nov., LM. 30–40. Eleven valves showing size diminution series. 30. Micrograph of holotype specimen. 32. Micrograph of isotype specimen. Scale bar = 10 μm.

FIGURES 41–46. Bacillaria dongtingensis sp. nov., colony and frustule view, SEM. 41. A colony. 42. Middle detail of Fig. 41, note raphe flange present on one side only (RF), one transapical rib forming two branches (arrow), and two transapical ribs merging into one (three curved arrows). 43.A dismantled frustule. 44. Middle part of Fig. 43, note raphe flange present on one side only (RF) and rudiments of marginal spines. 45, 46. Two apical details of Fig. 43, note raphe flange present on one side only (RF), T-shaped distal raphe ends, rudiments of marginal spines, and two girdle bands (B1 and B2). Scale bars =10 μm (Figs 41, 43), 2 μm (Fig. 42), 1 μm (Figs 44–46).

FIGURES 47–52. Bacillaria dongtingensis sp. nov., external view, SEM. 47. A complete valve. 48. Middle part detail of Fig. 47, note raphe flange present on one side only (RF), two transapical ribs merging into one (three curved arrows), and rudiments of marginal spines. 49. An apical detail of Fig. 47, note raphe flange present on one side only (RF) and T-shaped distal raphe end. 50. Another apical detail of Fig. 47, note one transapical rib forming two branches (arrow) and two transapical ribs merging into one (three curved arrows). 51. Other valve middle part, note one transapical rib forming two branches (arrow) and rudiments of marginal spines. 52. Other valve apex, note raphe flange present on one side only (RF) and one transapical rib forming two branches (arrow). Scale bar = 10 μm (Fig. 47), 3 μm (Figs 48–52).

FIGURES 53–58. Bacillaria dongtingensis sp. nov., internal view, SEM. 53. A complete valve. 54. Middle detail of Fig. 53 showing fibulae (F), two asymmetrical fibular ribs (FR), and two transapical ribs merging into one (three curved arrows). 55. Another apical detail of Fig. 53, note one transapical rib forming two branches (arrow) and two transapical ribs merging into one (three curved arrows). 56. Another apical detail of Fig. 53, note two asymmetrical fibular ribs (FR). 57. Other valve middle part, note one transapical rib forming two branches (arrow). 58. Other valve apex, note two fault sites (two arrows). Scale bar = 10 μm (Fig. 53), 2 μm (Figs 54–58).