Oricymba sinensis Bing Liu & Rioual, 2023

Yuan, Li, Liu, Bing, Rioual, Patrick, Yi, Man-Qi & Zheng, Yan, 2023, Two new species of Oricymba (Bacillariophyta) from China, described with reference to the structure of the apical pore field, Phytotaxa 591 (3), pp. 181-195 : 183-188

Oricymba sinensis Bing Liu & Rioual sp. nov. (LM: Figs 1–15 , SEM: Figs 16–39 )

Description:— LM: Valves dorsiventral possessing arcuate dorsal margin and slightly convex to straight ventral margin ( Figs 1–15 ). Apices not protracted or occasionally slightly protracted, bluntly rounded. Valve dimensions (n = 31): 36–52 μm long, 7.8–10.1 μm wide, length/width ratio range 4.2–5.5, median 4.9. Axial area narrow, lanceolate, expanded at central area. Raphe filiform. Proximal raphe endings deflected towards ventral side (primary side). Central pores present. Central area asymmetrical, occupying c. 1/3 of the valve width, flanked by c. 4 shortened ventral striae. A stigma evident on ventral side of valve. Striae radiate throughout valve, 9–11 in 10 μm in central portion of dorsal side, 9–12 in 10 μm in central portion of ventral side. Areolae difficult to resolve under LM.

SEM, external view: Valves asymmetric along apical axis, proximal raphe endings bent towards ventral side, and distal raphe fissures deflected towards dorsal side ( Figs 16 , 22 , 28 ). Marginal ridge evident along dorsal valve margin ( Figs 16–18, 20 , black arrows, see also Figs 22–24, 26 ) whereas marginal ridge inconspicuous along the ventral margin ( Figs 28–30, 32 , black arrows). External openings of areolae slit-like except those adjacent to axial area, which are curved or lunate ( Figs 23, 24, 26 , arrows). Dentate projections produced under each external opening of areola. Areola density 30–35 in 10 μm. Shallow depressions present in axial and central area ( Fig. 17 , white arrows). Apical pore field forming a continuous area, not divided by distal raphe fissure, clearly separated from areolae ( Figs 19, 21 ), composed of c. 5–8 transapical rows and 15–17 pervalvar rows. Foramina of apical pore field mostly rounded but a few top foramina elongate ( Figs 25, 27 , 31, 33 , arrows). A notch present on dorsal side of distal raphe fissure ( Figs 19, 21 , 31, 33 , wavy arrows, respectively). Valve mantle deep, meeting valve face at a right angle. Striae continuing onto valve mantle, but terminated before mid-line of valve mantle, such that abvalvar part of mantle without ornaments ( Figs 20, 21 , 29, 30, 32 , double-headed arrows, respectively). Girdle bands simple, c. three copulae per cell ( Fig. 21 ).

SEM, internal view: Valve asymmetric along apical axis, raphe straight, almost along valve mid-line, virgae and depressed striae alternate throughout valve ( Fig. 34 ). Proximal raphe endings not visible because obscured by flap above central nodule ( Fig. 35 , two wavy arrows) and distal raphe ends terminating in knob-like helictoglossae. Internally, stigma having two slit-like openings with fine ingrowths from perimeter ( Fig. 35 , two arrows). Areola internal openings occluded by dentate projections ( Figs 35, 36, 38 ). Apical pore field clearly separated from other parts of valve ( Fig. 37 , two arrows). An undulate flap-like silica strip covering internal apertures of each pervalvar row of foramina, not completely occluding internal apertures ( Fig. 39 , two arrows).

Type:— CHINA. Hunan province: Jianghua County, a sampling point from a headwater stream that runs into the Xiao River (25°4′24″ N, 111°50′54″ E, 380 m asl), Bing Liu , October 4 th 2021 (holotype JIU! Slide DIA202201 , specimen circled on slide = Fig. 1 ). Registration: http://phycobank.org/103643 .

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

Ecology:— Inhabiting surfaces of submerged stones, thus, belonging to river epilithon. In fresh waters, detailed information in Table 1 . This species was associated with Amphipleura vavilovii Glushchenko & Kulikovskiy (2017: 17) , and several unidentified species of Fragilaria Lyngbye (1819: 182) , Navicula Bory (1822: 128) , Cymbella Agardh (1830: 1) and Gomphonema Ehrenberg (1832: 87) .

Figures

FIGURES 1–15. Oricymba sinensis sp. nov., LM. Valves arranged in a size diminution series. Note the conspicuous dorsiventrality. Fig. 1 corresponds to the holotype specimen. Scale bar = 10 μm (in Fig. 1).

FIGURES 16–21. Oricymba sinensis sp. nov., SEM external view. 16. A tilted frustule, note a marginal ridge present on the dorsal side of valve (three black arrows). 17. Detail from Fig. 16, note the marginal ridge (two black arrows) and shallow depressions in the axial and central area (white arrows). 18, 20. Apical details from Fig. 16, note the marginal ridge (two black arrows), the valve face and the mantle almost met at a right angle, and the abvalvar part of mantle without ornaments (Fig. 20, double-headed arrow). 19, 21. Details from Fig. 18 and Fig. 19, respectively, note a notch on the dorsal side of distal raphe fissure (wavy arrows), the differentiated apical pore field clearly separated from the areolae (straight arrows), and the abvalvar part of mantle without ornaments (double-headed arrows). Scale bars = 5 μm (Fig. 16), 1 μm (Figs 17–21).

FIGURES 22–27. Oricymba sinensis sp. nov., SEM external view. 22. A slightly tilted frustule, note the lateral raphe. 23, 24, 26. Details from Fig. 22, note the areola openings curved or lunate adjacent to the axial area (arrows). 25, 27. Apical details from Fig. 24 and Fig. 26 respectively, note the top foramina of apical pore field are elongate (arrows), which are different from the other rounded foramina. Scale bars = 5 μm (Fig. 22), 1 μm (Figs 23–27).

FIGURES 28–33. Oricymba sinensis sp. nov., SEM external view. 28. A tilted frustule, note the marginal ridge on the ventral side of valve is inconspicuous (three black arrows). 29, 30, 32. Details from Fig. 28, note the marginal ridge on the ventral side of valve is very slightly raised (arrows). 31, 33. Apical details from Fig. 30 and Fig. 32 respectively, note the top foramina of apical pore field are elongate (arrows), which are different from the other rounded foramina. Scale bars = 5 μm (Fig. 28), 1 μm (Figs 29–33).

FIGURES 34–39. Oricymba sinensis sp. nov., SEM internal view. 34.A complete valve, note the internal straight raphe fissure.35. Middle part from Fig. 34, note two slit-like openings of stigma (two arrows) and the proximal raphe endings not visible as they are obscured by flap above central nodule (two wavy arrows). 36, 38. Apical details from Fig. 34, note the areola internal openings occluded by dentate projections. 37. Detail from Fig. 36, note the apical pore field clearly separated from the other parts of valve (two arrows). 39.Apical detail from another valve not included in this plate, note an undulate flap-like silica strip covering the internal apertures of each pervalvar row of foramina, not completely occluding internal apertures (two arrows). Scale bars = 5 μm (Fig. 34), 1 μm (Figs 35–39).