Ctenophora hunanensis Bing Liu & Rioual 2024, sp. nov.

Ctenophora hunanensis Bing Liu & Rioual sp. nov. Figs 2, 3, 4, 5 Holotype. Specimen circled on slide DIA 2024010 (= Fig. 2 B), deposited in the Herbarium of Jishou University (JIU), China. Registration: http://phycobank.org/105130. Type locality. China. Hunan Province: Anren County, Yongle River, sampling site with the coordinates 26°50'12"N, 113°35'59"E, and an elevation of 123 m asl. Diatom samples collected by Bing Liu, March 24, 2024. Description. LM (Fig. 2). Valves lanceolate with rostrate apices. Valve dimensions (n = 30): length 48–78 μm, width 6.5–8.5 μm at center. Sternum clearly visible, gradually widening when approaching central area. Central area distinct, rectangular to square, sometimes with ghost striae. Striae parallel, uniseriate, perpendicular to central sternum, opposite one another across sternum. Stria density 13–16 in 10 μm. Areolae punctate, 20 in 10 μm. Many abnormal valves are found, all of which exhibit the asymmetry relative to the apical axis due to the V-shaped incising of valve margin only occurring at one side (Fig. 2 C, E, H). SEM (Figs 3 – 5). Sternum meeting and integrated with virgae, vimines reduced in size relative to virgae. Virgae and vimines join to form square to rectangular areolae that are closed externally by complex cribra appearing as sieve-like closing plates composed of pegged struts (Fig. 3 D – F). Inner openings of areolae appear rounded (Fig. 4 C, D). Central area distinctive, externally a broad plain area (Fig. 3 D), internally thickened around its periphery, ghost striae within (Fig. 4 D). One rimoportula present at each apex, externally expressed as a simple hole (Fig. 3 E, F), internally bilabiate, situated close to sternum (Fig. 4 E, F). Ocellulimbus produced at each apex, typically sunken below surface of valve margin (Fig. 3 E, F). Valvocopula open, lacking ornamentation, distinctly deeper than copulae (Fig. 5). On its advalvar edge, valvocopula bears a row of serrated projections, each corresponding internally to a virga (Fig. 5, three arrows). Copulae with row of poroids situated at pars media (Fig. 5, two wavy arrows). Etymology. Named after Hunan Province where the species was found. Distribution and ecology. Known only from the type locality. The samples that included this species were scraped off the surface of stones collected in the Yongle River. Hence this is a benthic, epilithic species. The relative abundance of this new species is ca. 3 %. The associated taxa include Gomphonema parvulum (Kützing) Kützing, Luticola spp., Planothidium frequentissimum (Lange-Bertalot) Lange-Bertalot, Tryblionella spp., Nitzschia spp., among others. The following environmental parameters were measured in the field with three replications: Conductivity = 85.9 ± 0.1 μS cm - 1; pH = 8.9 ± 0.1; Water temperature = 22.3 ± 0.3 ° C.