Diploneis distinctebipunctata Jovanovska & Wilson & Hamilton & Stone 2023, sp. nov.

Diploneis distinctebipunctata sp. nov. (LM Figs 549–560, SEM Figs 561–566) Valves are weakly asymmetric, elliptic-lanceolate becoming elliptic-circular with smaller cell size (Figs 549–561). Valve length is 28–57 μm and width is 18–26 μm. The axial area is narrow, linear to lanceolate, patterned with irregular round ornamentations opening into small depressions that do not penetrate the silica cell wall (white arrow Fig. 562). The axial area slightly widens into a longitudinally elongate and weakly asymmetric central area (Figs 549, 561, 565), 3–6 μm wide. Externally, the canal is linear to lanceolate, slightly expanded in the middle of the valve with two (three) rows of cribrate (>40 poroids) areolae narrowing into one larger at the valve apices (Figs 549–552, 561). Internally, a thick non-porous slightly raised silica plate encloses the longitudinal canal (Fig. 566). Externally, the raphe is filiform, curved; the proximal ends are deflected to one side within expanded teardrop depressions (Figs 561, 565). The distal raphe ends are unilaterally bent to the same side as the proximal ends and terminate on the upper section of the mantle (Figs 561, 562). Internally, the raphe is curved and placed in the depression formed by the longitudinal canal (Fig. 566). The striae are parallel at mid-valve becoming radiate towards the apices, 8–10 in 10 μm. Striae are biseriate throughout (Figs 563, 564). The striae are composed of round areolae covered externally with fine pored cribra (>40 poroids), 15–18 in 10 μm. Internally, the alveoli open via a single elongated opening covered with a thin silica layer (Figs 564, 566). The valvocopula has serrated advalvar edges (Fig. 566). Type:— REPUBLIC OF ZAMBIA, Mulungushi River, at 1117 m elevation; mud, 0.1 m water depth, 14°17’45.6” S 28°32’54.8” E, E. Jovanovska & Z. Levkov, 27 th September 2021 (holotype designated here, circled specimen BM-108976! = Fig. 552, isotypes ANSP-GC17205!, CANA-130011!). Type material CANA-129322. Registration: http:// phycobank.org/103705 Pictures of the isolated specimen:— LM micrograph on 1000× magnification (Fig. S 3m). Sequence data:— Plastid gene rbc L sequence (GenBank accession: OQ 660300). Etymology:— The specific epithet ‘ distinctebipunctata ’ refers to the visible biseriate nature of the striae under LM observation. Ecology and distribution:— This species has only been observed in the Mulungushi River and Kalambo River and in the fossil deposits of Lake Malawi (unpublished data). The Mulungushi River, from where this species was described, has a moderately alkaline pH (7.9), a low conductivity of 101 μS̔ cm-1, and low water transparency. It cohabits with the species Diploneis dissipata sp. nov. and Diploneis latissima sp. nov. Main differential characters:— Valve width and shape, striae pattern, narrow canals, surface depressions along axial area, and poroids>40 per areola. Similar species:— Diploneis lusatica and Diploneis amicula Kulikovskiy & Lange-Bertalot (2015: 86).

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