Oricymba fanjingensis 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 : 188

Oricymba fanjingensis Bing Liu & Rioual sp. nov. (LM: Figs 40–53 , SEM: Figs 54–71 )

Description:— LM: Valves asymmetric to apical axis, dorsiventral with dorsal margin a little more arcuate than ventral margin ( Figs 40–53 ). Apices apiculate. Valve dimensions (n = 36): 34–59 μm long, 9.9–14.6 μm wide, length/width ratio range 3.2–4.7, median 4.0. Axial area narrow, rhombic-lanceolate, expanded at oval central area. Raphe filiform. Proximal raphe endings deflected towards ventral side. Central pores present. Central area asymmetrical, small, occupying c. 1/4 of the valve width, flanked by c. 3 or 4 shortened ventral striae and 1 or 2 shortened dorsal striae. A stigma evident on ventral side of valve. Striae slightly radiate throughout valve, 8–10 in 10 μm in central portion of dorsal side, 7–11 in 10 μm in central portion of ventral side. Areolae easily resolved under LM, 20–24 in 10 μm.

SEM, external view: Valves asymmetric along apical axis, proximal raphe endings clearly bent towards ventral side, and distal raphe fissures deflected towards dorsal side ( Figs 54 , 60–62 ). Marginal ridges evident along both dorsal and ventral valve margins ( Fig. 54 , four arrows; Figs 55–57 , two arrows). Two valve surface ridges produced ( Fig. 54 , four wavy arrows; Figs 55–57 , two wavy arrows), each parallel to each marginal ridge, thus two grooves formed ( Figs 55–57 , 63–65 , two double-headed arrows). External openings of areolae mostly slit-like. Dentate projections produced under each external opening of areola. Apical pore field forming a continuous area, not divided by distal raphe fissure, clearly separated from areolae ( Figs 58, 59 ), composed of c. 5–8 transapical rows and 12–14 pervalvar rows. Foramina of apical pore field mostly rounded, a notch on dorsal side of distal raphe fissure is present ( Figs 58, 59 , arrow, respectively). Valve mantle deep, meeting valve face at a right angle ( Figs 66, 67 ). Striae continuing onto valve mantle, but terminated before mid-line of valve mantle, such that abvalvar part of mantle without ornaments.

SEM, internal view: Valve slightly asymmetric along apical axis with apiculate apices, raphe straight, almost along the valve mid-line, virgae and depressed striae alternate throughout valve ( Figs 66, 67 ). Proximal raphe endings not visible because obscured by flap above central nodule ( Fig. 68 , wavy arrow) and distal raphe ends terminating in knob-like helictoglossae ( Figs 69–71 ). Internally, stigma having two slit-like openings, both with fine ingrowths from perimeter ( Fig. 68 , two arrowheads). Areola internal openings occluded by dentate projections ( Figs 68–70 ). Apical pore field clearly separated from other parts of valve ( Fig. 71 ).

Type:— CHINA. Guizhou Province: Jiangkou County, sampling point from a headwater stream that runs into the Dajiang River (27°49′48″ N, 108°45′53″ E, 500 m asl), Bing Liu , December 31 st 2015 (holotype JIU! Slide DIA202202 , specimen circled on slide = Fig. 40 ). Registration: http://phycobank.org/103644 .

Etymology:— Named after Fanjing Mountain, 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 Achnanthidium sinense Bing Liu & Blanco (in Liu et al., 2016: 195), A. minutissimum (Kützing) Czarnecki ( Czarnecki 1994: 157) , and several unidentified species of Ulnaria (Kützing) Compère (2001: 100) and Encyonema Kützing (1834: 529) .

Figures

FIGURES 40–53. Oricymba fanjingensis sp. nov., LM. 40–53. 14 valves showing a size diminution series, note the apiculate valve apices. Fig. 40. Illustration of holotype specimen. Scale bar = 10 μm (in Fig. 1).

FIGURES 54–59. Oricymba fanjingensis sp. nov., SEM external view. 54. A complete valve, note two marginal ridges (four arrows) and two valve surface ridges (four wavy arrows). 55–57. Details from Fig. 54, note the marginal ridges (arrows), valve surface ridges (wavy arrows), and a groove between the marginal ridge and its adjacent surface ridge (double-headed arrows). 58, 59. Apical details from Fig. 54, note a notch on the dorsal side of distal raphe fissure (two arrows), the differentiated apical pore field clearly separated from the areolae. Scale bars = 5 μm (Figs 54, 56–57), 1 μm (Figs 55, 58–59).

FIGURES 60–65. Oricymba fanjingensis sp. nov., SEM external view. 60–62. Three complete valves, note the marginal ridges and its adjacent surface ridges. 63–65. Details from Fig. 62, note a groove between two adjacent ridges (double-headed arrows). Scale bars = 5 μm (Figs 60–62), 1 μm (Figs 63–65).

FIGURES 66–71. Oricymba fanjingensis sp. nov., SEM internal view. 66, 67. Two complete valves. 68. Middle part from Fig. 66, note two slit-like openings of stigma (two arrows) and the central raphe endings invisible because obscured by flap over central nodule (wavy arrow). 69, 70.Apical details from Fig. 66, note the areola internal openings occluded by dentate projections and the marginal ridges (four arrows). 71. Detail from Fig. 70, note the internal apertures of each pervalvar row of foramina. Scale bars = 5 μm (Figs 66–67), 1 μm (Figs 68–71).