Aulacoseira huguang He, Rioual & Wang, 2023

He, Wenyu, Rioual, Patrick, Luo, Hai, Li, Jingjing & Wang, Luo, 2023, Aulacoseira huguang sp. nov., a new Lateglacial fossil diatom from South China, Phytotaxa 629 (3), pp. 223-234 : 225-226

Aulacoseira huguang He, Rioual & Wang sp.nov. (LM: Figs 2–55 , SEM: Figs 56–67 )

Species description:—LM observations ( Figs 2–55 ): Cells cylindrical, solitary or forming short chains composed of 2 cells. Valve diameter 3.9–6.2 µm, mantle height 2.1–3.2 µm (n = 27). Ratio between mantle height and diameter varies from 0.27 to 0.54. Pervalvar rows of areolae 14–20 /10 µm. A row of spines occurs around the circumference of the valve face. The arrangement of areolae on the surface of the valve mantle is slightly dextrose. On the valve face the areolae are evenly spaced without a clear pattern. Rimoportulae not conspicuous under the light microscope.

SEM observations ( Figs 56–67 ): On the slightly convex mantle ( Figs 56, 64 ), areolae generally circular in shape but elongated near the collum. Areolae generally small, their size decreasing from the collum towards the valve face ( Figs 58–62 ). Areolae with simple structure ( Fig. 64 ). Valve face flat or slightly concave with round areolae evenly spaced over the entire surface, smaller at the centre of the valve than near the edges ( Figs 58–64 ). The surface of the collum is smooth only ornamented by a row of tiny siliceous nodules generally positioned at the basis of the ribs ( Figs. 56, 57, 63 ). On the surface of mantle ribs, siliceous nodules are randomly distributed ( Figs 56, 57, 63 ). The spines are conical, stout at the base and bluntly rounded at the tip, raised from two ribs on the mantle ( Figs. 56, 57, 64 ). Spine length of about 1/5–1/4 of the valve height. Spines slightly curve towards the outside, separated from each other by areolae. Only separating spines were observed. Ringleist 1.2–1.5 µm in width, shelf-like, projecting far into the cell interior, thicker at its inner edges ( Figs 57, 63 ). Rimoportulae, two per valve, located in the ringleist, sessile, extending from mantle to about 1/2 to 2/3 of the ringleist and placed in opposite positions on the perimeter of the valve ( Figs. 56, 57, 64–66 ).

Holotype:— The holotype slide ( IGGDC-HGY-A5-189 ) is deposited at the Herbarium of Bacillariophyceae, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, People’s Republic of China (the herbarium acronym, IGGDC, follows the Index Herbariorum of the New York Botanical Garden and is listed at https:// sweetgum.nybg.org/science/ih/). The holotype specimen is illustrated in Figs 45–47 , and can be located on the slide using England Finder L47/1 or at the coordinates 11.2 S and 4.5 E following the method described by Sterrenburg et al. (2012).

Isotype:— An isotype slide BM 98365 is deposited in the collection of the Natural History Museum, London, United Kingdom.

Type locality:— China, Guangdong province, Zhanjiang municipality, Huguangyan maar lake, sampling point (21°8’39.77’’N, 110°16’39.72’’E, 90 m a.s.l.). Fossil material from sediment samples dated to the Lateglacial (from 17,000 to 10,000 years BP). Type sample corresponding to core depth 896 cm, dated to ~10,280 years before present. Collected by Dr Luo Wang on 10 th September 2010.

Etymology: —Named after the lake where the species was found.

Associated diatom flora:— The diatom assemblage in the holotype slide (IGGDC-HGY-A5-189) is composed of Discostella stelligera (49%) (Cleve et Grunow) Houk & Klee (2004: 208); A. huguang (24%) He, Rioual & Wang; A. granulata (12%) (Ehrenberg) Simonsen (1979: 58); Achnanthidium minutissimum (4%) (Kützing) Czarnecki (1994: 157); Encyonema neogracile (2%) Krammer (1997: 177); Navicula heimansii (1.5%) Van Dam & Kooyman (1982: 1); Achnanthes acares (1%) Hohn & Hellerman (1963: 273).

Figures

FIGURES 2–55. LM images of Aulacoseira huguang sp. nov., taken from the holotype population (sample HGY-A5-189) under bright field and DIC (except for Figs 10–11, taken under phase contrast). 2–25. Valve views, each specimen is seen under two different focus plans. 26–31. Girdle views of single valves showing the range in mantle height. 32–51. Girdle views of complete frustules, each specimen seen under two or three different focus plans. 54–55. Short chain composed of two frustules in girdle view. Scale bar = 5 µm. Figs 45–47 correspond to the holotype specimen.

FIGURES 56–67. SEM images of Aulacoseira huguang, taken from the holotype population (sample HGY-A5-189) Fig. 56. Oblique view of a single valve showing from the top to the bottom of the valve: the row of spines that occurs around the circumference of the valve face, the pervalvar rows of areolae slightly dextrorse, the smooth collum with tiny nodules, the ringleist, projecting deep into the valve interior. Fig. 57. Mantle view of a single valve showing the pervalvar rows of areolae slightly dextrorse, the smooth collum with tiny nodules and external opening of one rimoportula (arrow). Fig. 58. Oblique view of a complete frustule, showing the pervalvar rows of areolae slightly dextrorse, the smooth collum with tiny nodules and external opening of one rimoportula (arrow). Fig. 59. Oblique view showing the valve face with evenly spaced areolae, decreasing in size from the edges to the centre of the valve. An areola is positioned between each spine. Figs 60–62. External views of partly corroded valves showing round areolae of various size. Fig. 63. Ringleist view. Fig. 64. Girdle view showing conical spines, stout at the base and bluntly rounded at the tip, raised from two ribs on the mantle. Siliceous nodules are visible on the collum at the basis of each rib, with more nodules on the ribs. Fig. 65. Internal view of a broken valve. The internal opening of one rimoportula (arrow) is visible on the ringleist. Fig. 66. External view of a broken frustule. In the broken valve, both rimoportulae are visible. They are placed in opposite positions on the perimeter of the valve (arrows). Fig. 67. Internal view of a broken valve showing the internal openings of two rimoportulae (arrows) which are visible on the ringleist. The two rimoportulae are placed in opposite positions on the perimeter of the valve. Scale bars = 3µm.