Diploneis nana, Jovanovska & Wilson & Hamilton & Stone, 2023

Jovanovska, Elena, Wilson, Mallory C., Hamilton, Paul B. & Stone, Jeffery, 2023, Morphological and molecular characterization of twenty-five new Diploneis species (Bacillariophyta) from Lake Tanganyika and its surrounding areas, Phytotaxa 593 (1), pp. 1-102 : 54

Diploneis nana sp. nov. (LM Figs 299–319 , SEM Figs 320–322 )

Valves are weakly asymmetric, linear-elliptic to elliptic with weakly convex margins and slightly acute apices ( Figs 299–320 ). Valve length is 17.5–32.5 μm and valve width is 8.5–11.5 μm. The axial area is very narrow, linear to lanceolate, widening into a slightly longitudinally elongate to indistinguishable and weakly asymmetric central area ( Figs 300, 320, 322 ), 1.5–2.7 μm wide. Externally, the canal is linear to lanceolate, slightly expanded in the middle of the valve with two (rarely three) rows of cribrate (9–15 poroids) areolae narrowing into one at the valve apices ( Fig. 320 ). Internally, a thick non-porous slightly raised silica plate encloses the longitudinal canal ( Fig. 321 ). Externally, the raphe is filiform, curved with strongly deflected and expanded proximal ends. The proximal raphe ends are positioned within an elongated surface depression ( Fig. 322 ). The distal raphe ends are unilaterally bent to the same side and extend onto the mantle ( Fig. 320 ). Internally, the raphe branches are slightly arched with simple proximal and distal ends that are slightly elevated in a depression formed by the longitudinal canal ( Fig. 321 ). The striae are parallel at mid-valve becoming radiate towards the apices, 11–13 in 10 μm. Striae are uniseriate throughout ( Figs 320, 322 ). The striae are composed of round areolae covered externally with fine pored cribra (20–33 poroids), 20 in 10 μm. The inter-areolar thickenings have scattered fin-like silica ridges serrated with ca. 4–5 notched edges. The areolae increase in size towards the valve margins ( Fig. 320 ). Internally, the alveoli open via a single elongated opening covered with a thin silica layer ( Fig. 321 ).

Type:— UNITED REPUBLIC OF TANZANIA, Lake Tanganyika , Mahale National Park, at 780 m elevation; sand, 30 m water depth, collected SCUBA diving, 6°10’25.1” S 29°44’25.2” E, W. Salzburger, 28 th June 2019 (holotype designated here, circled specimen BM-108996! = Fig. 306 , isotypes ANSP-GC17225 !, CANA-129317!). Type material CANA-129317. Registration: http://phycobank.org/103715

Pictures of the isolated specimen:— LM micrograph on 1000× magnification ( Fig. S3w ).

Sequence data:— Plastid gene rbc L sequence (GenBank accession: OQ 660277).

Etymology:— The specific epithet ‘ nana ’ or dwarf highlights relatively small size of this taxon among Diploneis species in Lake Tanganyika.

Ecology and distribution:— This species has only been observed in Lake Tanganyika in the three sub-basins on the Tanzanian and Zambian sides. Despite its small size, this species is never abundant in the alkaline, moderately mineral-rich and highly transparent lake. It is typically found on sandy substrates (sometimes with mollusk shells) or submerged rocks between 9 and 36 m water depth. It is mainly found in Mahale National Park, but also in Kiganza Bay in the north and in Isanga Bay, Mutondwe Island, and Cape Nangu at Kasaba Bay in the south. The small species usually occurs together with D. kilhamiana sp. nov., D. cocquytiana sp. nov., D. salzburgeri sp. nov., D. disjuncta sp. nov., D. clara sp. nov., D. serrulata sp. nov., and D. cristata sp. nov.

Main differential characters:— Valve size and shape, central area, external fin-like ornamentations across the valve, and recessed areolae over the canals.

Similar species:— Diploneis disjuncta sp. nov. and Diploneis nevrovae Lange-Bertalot & Fuhrmann (2020: 89) .

Figures

FIGURES 299–322. Diploneis nana sp. nov., LM (Figs 299–319), SEM external (Figs 320, 322), and internal (Fig.321) valve views, Lake Tanganyika. 299–302, 304, 306–308, 310–312, 315–318. Specimens from the type material, Mahale National Park. 303, 319. Specimens from Isanga Bay. 305, 309, 313, 314, 320–322. Specimens from Kiganza Bay. Fig. 306. Holotype specimen. Fig. 320.Valve view, showing canal structure, striae structure, and inter-areolar fin-like silica ridges. 321. Valve view, showing simple raphe branch and alveoli occluded by thin silica layers. 322. Detail central area with teardrop shaped depressions with proximal raphe ends bent to the same side of the valve; white arrowed inter-areolar fin-like shaped ornamentations. Scale bars = 10 μm (Figs 299–319), 5 μm (Figs 320, 321), 2 μm (Fig. 322).

FIGURES 2–11. Diploneis salzburgeri sp. nov., LM valve views, Lake Tanganyika. 2, 3, 5, 6, 9. Specimens from southern parts of Lake Tanganyika, Kalambo Falls Lodge. 4. Specimen from Kalya Bay. 7. Specimen from Ndole Bay. 8. Specimen from Jakobsen Beach, near Kigoma. 10, 11. Specimens from Buhingu Island. Fig. 7. Holotype specimen. Scale bar = 10 μm.