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

Diploneis dissipata sp. nov. (LM Figs 518–543, SEM Figs 544–548) Valves are weakly asymmetric, linear-elliptic with parallel to weakly convex margins and round apices (Figs 518– 544). Valve length is 18.5–40 μm and width is 11–14 μm. The axial area is narrow, lanceolate, slightly expanding into a longitudinally elongate and weakly asymmetric central area (Figs 518, 544), 2.7–3 μm wide. Externally, the canal is linear to lanceolate, slightly expanded in the middle of the valve with three rows of cribrate (<6 poroids) areolae narrowing into one at the valve apices (Figs 518, 544, 545). Internally, a thick non-porous slightly raised silica plate encloses the longitudinal canal (Fig. 546). Externally, the raphe is filiform, curved; the proximal ends are curved to one side and positioned within an expanded teardrop depression (Fig. 545). The distal raphe ends are unilaterally bent to the same side as the proximal ends and terminate on the valve face (Fig. 544). Internally, the raphe is curved with simple proximal and distal ends that are slightly elevated within a depression formed by the longitudinal canal (Figs 546–548). The striae are parallel at mid-valve becoming radiate towards the apices, 10–11 in 10 μm. Striae are biseriate throughout (Figs 545, 547). The striae are weakly depressed and composed of round areolae covered externally with cribra (9–16 poroids), 20 in 10 μm. The inter-areolar thickenings have longitudinal fin-like silica ridges serrated with ca. 5–10 notched edges. The areolae increase in size towards the valve margins (Fig. 545). Internally, the alveoli open via a single elongated opening covered with a thin silica layer (Fig. 547). 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-108977! = Fig. 526, isotypes ANSP-GC17206!, CANA-130012!). Type material CANA-129322. Registration: http:// phycobank.org/103704 Pictures of the isolated specimen:— LM micrograph on 1000× magnification (Fig. S2l). Sequence data:— Plastid gene rbc L sequence (GenBank accession: OQ 660284). Etymology:— The specific epithet ‘ dissipata ’ refers to the extended distribution of Diploneis dissipata sp. nov., which occurs both inside of and outside of Lake Tanganyika, and has the characteristic valve face fin-like ridges. Ecology and distribution:— This species has been observed in Lake Tanganyika and Mulungushi River. This is the only species we have found outside Lake Tanganyika that thrives in a less alkaline (pH = 7.9 vs. 8.5–9.1 in Lake Tanganyika), lower conductivity of 101 μS̔ cm-1 (vs. 600–700 in Lake Tanganyika), and less transparent environment. Diploneis dissipata sp. nov. is very rare in Lake Tanganyika and restricted to the central sub-basin in the Rukoma area on sandy substrates in about 10 m water depth, together with D. kilhamiana sp. nov., D. cocquytiana sp. nov., D. tessellata sp. nov., D. angusta sp. nov., D. serrulata sp. nov., and D. cristata sp. nov. In contrast, the species is more common in the Mulungushi River in the muddy areas along with D. distinctebipunctata sp. nov. and Diploneis latissima sp. nov. Main differential characters:— Valve shape, striae pattern, narrow canals, external fin-like ornamentations across the valve, poroids within thickenings along the canals, and poroids <16 per areola. Similar species:— Diploneis voigtiana Lange-Bertalot & Fuhrmann (2020: 138).

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