Diploneis fossa, 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 : 40

Diploneis fossa sp. nov. (LM Figs 178–185 , SEM Figs 186–192 )

Valves are weakly asymmetric, elliptical to linear–elliptical with parallel margins and bluntly round apices ( Figs 178–188 ). The length of the valve is 47.5–64 μm and the width of the valve is 23–27 μm. The axial area is narrow, lanceolate, widening at the center to form a longitudinally elongate and weakly asymmetric central area ( Figs 178 , 187, 190 ), 4–5 μm wide. Externally, the canal is lanceolate and slightly expanded in the middle of the valve with three rows of cribrate (<15 poroids) areolae narrowing into one at the valve apices ( Fig. 189 ). Externally, the raphe is filiform, curved with simple proximal ends bent to the same side of the valve; the proximal fissures are positioned in expanded teardrop depressions ( Figs 187, 190 ). The distal raphe ends are unilaterally bent to the same side and terminate at the valve face mantle junction ( Figs 188, 189, 192 ). The striae are parallel at mid-valve becoming radiate towards the valve apices, 8–9 in 10 μm. Striae are uniseriate throughout ( Figs 189, 191 ). The striae are composed of large round to rectangular areolae covered externally with fine pored cribra (>45 poroids), 8–10 in 10 μm. Externally, each areola opens into deep pits. The inter-areolar thickenings have fin-like crest silica ridges serrated with ca. 9–12 fine notched edges ( Fig. 189 ). The fin-like ridges along the canal are slightly bent into semi-circular shape, positioned towards the striae whereas those of the striae are only slightly bent positioned towards the canal, changing opposite direction only at valve mantle ( Figs 187, 192 ).

Type:— REPUBLIC OF ZAMBIA, Lake Tanganyika , Isanga Bay, at 768 m elevation; rock scrape, 20 m water depth, collected SCUBA diving, 8°39’10.7” S 31°11’34.8” E, A. Jordan, 8 th October 2021 (holotype designated here, circled specimen BM-108982! = Fig. 184 , isotypes ANSP-GC17211 !, CANA-129334!). Type material CANA-129329. Registration: http://phycobank.org/103708

Pictures of the isolated specimen:— LM micrograph on 1000× magnification ( Fig. S2c ).

Sequence data:— Plastid gene rbc L sequence (GenBank accession: OQ 660301).

Etymology:— The specific epithet ‘ fossa ’ refers to the ditch-like formation of the fin-like crest ridges.

Ecology and distribution:— This species has only been observed on the Zambian and Tanzanian coasts of Lake Tanganyika. In the alkaline, moderately mineral-rich and highly transparent waters, it inhabits sandy and muddy substrates (sometimes with mollusk shells) and submerged rocks between 5 and 33 m water depth. The largest population sizes of this species have been found in the southern parts of the lake in Isanga Bay and Mutondwe Island. Smaller population sizes were found in Chituta Bay, Kalambo Falls Lodge, Ndole Bay and in the central parts of the lake in Kalya Bay and Mahale National Park ( Fig. 1c, e, f ). In the type material, it mostly coexists with D. major sp. nov. while at all other sites it occurs with D. kilhamiana sp. nov., D. cocquytiana sp. nov., D. tumida sp. nov., D. cristata sp. nov., D. salzburgeri sp. nov., D. serrulata sp. nov., and D. duplex sp. nov.

Main differential characters:— Valve shape, striae pattern, striae density, external fin-like ornamentations across the valve, fins scattered on the longitudinal canals, areolae formation over the longitudinal canal (thickened virgae), and poroids>45 per areola.

Similar species:— Diploneis elongata sp. nov. and Diploneis raetica Lange-Bertalot & Fuhrmann (2020: 119) .

Figures

FIGURE 1. Maps ofAfrica with major drainage systems. a) Map of Africa indicating the general location of the East African Rift (framed in bold grey lines). b) Map of East African Rift with sample (purple circles) and type (green circles) localities for all twenty-five new Diploneis species. c) Bathymetric map of the three sub-basins of Lake Tanganyika with close-up of sampling sites in the lake. d) Key sampling sites in the northern Kigoma sub-basin of Lake Tanganyika. e) Key sampling sites in the central Kundwe sub-basin of Lake Tanganyika. f) Key sampling sites in the southern Kipili sub-basin of Lake Tanganyika. Location details for each species are given in the descriptions.

FIGURES 178–185. Diploneis fossa sp. nov., LM valve views, Lake Tanganyika. 178, 179, 181, 182. Specimens from Mutondwe Island. 180, 183–185. Specimens from Isanga Bay. Fig. 184. Holotype specimen. Scale bar = 10 μm.

FIGURES 186–192. Diploneis fossa sp. nov., SEM external valve views, Lake Tanganyika.186, 187, 191, 192.Specimens from Mutondwe Island. 188–190. Specimen from Kiganza Bay. 186–188. View of a whole valve. 189. Detail valve apices, showing distal raphe ends with deflected terminal fissures and large round to rectangular areolae opened in deep pits. 190. Central area with teardrop depression with proximal raphe ends. 191. Close view of the areolae separated from each other with inter-areolar thickenings bearing fin-like silica ridges. 192. Distal raphe ends with deflected terminal fissures. Scale bars = 10 μm (Figs 186–188), 5 μm (Fig. 192), 2 μm (Figs 189, 191), 1 μm (Fig. 190).

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.