Planothidium pseudolinkei Lang Li, Yuhang Li & Junxiang Lai 2024, sp. nov.

Planothidium pseudolinkei Lang Li, Yuhang Li & Junxiang Lai sp. nov. Figs 2, 3, 4 Holotype. Slide MBMCAS 286907 deposited in the Marine Biological Museum, Chinese Academy of Sciences (MBMCAS), Qingdao, China, represented here by Fig. 2 B (Rapheless valve) and Fig. 2 H (Raphe valve). Type locality. Jin Beach, Wanwei Island, Guangxi Province, China, 21 ° 31.85 ′ N, 108 ° 10.95 ′ E, surface sand samples, collected by Lang Li on 10 January 2021. Description. LM (Fig. 2 A – L). Valves lanceolate to elliptic-lanceolate with convex margins and protracted, capitate to rostrate apices. Valve dimensions (n = 75): length 26.5–50.0 μm, width 10.0–13.0 μm. Rapheless valve (Fig. 2 A – F): Axial area linear and narrowly lanceolate, slightly expanded in the middle of the valve. Central area asymmetrical with a unilateral large hyaline area; on the opposite side, striae barely shortened near the axial area. Striae weakly radiate at the center and more strongly radiate towards the apices, 11–12 in 10 μm. Raphe valve (Fig. 2 G – L): Axial area very narrow, linear, slightly widened near the middle of the valve. Central area very small, slightly transapically expanded, bordered by 3–4 shortened striae on each side. Raphe straight, filiform with slightly enlarged central raphe endings. Terminal fissures not discernible in LM. Striae radiate throughout the entire valve, 12 in 10 μm. Areolae not discernible in LM. SEM (Figs 3 A – F, 4 A – F). Rapheless valve (Fig. 3 A – F): Externally, valve face generally flat, with a slightly linear depression in the axial area (Fig. 3 A). Central area large, unilateral (Fig. 3 A, B). Striae multiseriate, composed of three rows of small, rounded areolae at the apices, varying from three rows near the valve face / mantle junction to biseriate towards the axial area (Fig. 3 B, C). Striae portion near the axial area often composed of one or two areolae (Fig. 3 B). Striae extending onto the valve mantle, but interrupted by the valve face-mantle junction (Fig. 3 B, C). Internally, axial area elevated and striae sunken between the raised virgae (Fig. 3 D – F). A well-developed sinus distinctly present on one side of the central area, with the borders fusing with lateral virgae, forming a deep oblong depression (Fig. 3 D, E). Raphe valve (Fig. 4 A – F): Externally, valve face flat (Fig. 4 A). Striae composed of one to four rows of small, rounded areolae, clearly broader than virgae at the apices (Fig. 4 B, C). Striae portion along the axial area composed of two larger areolae than other ones (Fig. 4 B, C). Central raphe endings straight, simple, expanded and pore-like (Fig. 4 B). Terminal fissures bent, continuing shortly onto the valve mantle (Fig. 4 C). Internally, virgae poorly developed (Fig. 4 D – F). Raphe hook-shaped, branches situated on a slightly elevated raphe-sternum (Fig. 4 D). Terminal raphe endings terminated by small helictoglossae (Fig. 4 F). Etymology. The specific epithet, pseudolinkei, was referring to the morphological and habitat similarities with P. linkei. PhycoBank registration. http://phycobank.org/104835. Distribution and ecology. In addition to the type locality, P. pseudolinkei also occurs in the surface sand sample from the Bailang Beach of Jiangshan Peninsula. This taxon is a marine epipsammic diatom. In the type material, P. pseudolinkei was very rare and only found in abundance of 0.14 %. The associated diatom flora is composed of Amphora spp., Navicula spp., Diploneis spp., Fallacia spp., Cocconeiopsis spp., Gyrosigma sp., Planothidium sp., Anorthoneis hummii Hustedt, Biremis ambigua (Cleve) D. G. Mann, Cymatoneis margarita A. Witkowski, Moreneis coreana J. Park et al. and Halamphora coffeiformis (C. Agardh) Levkov.