Diploneis latiuscula, 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 : 26

Diploneis latiuscula sp. nov. (LM Figs 85–96 , SEM Figs 97–107 )

Valves are weakly asymmetric, broadly lanceolate to rhombic-elliptic with convex margins and bluntly round apices ( Figs 85–97 ). Valve length is 34.5–47 μm and valve width is 19.5–26.5 μm. The axial area is narrow, lanceolate, slightly expanding into a small to indistinguishable and weakly asymmetric central area ( Fig. 85 ), 4–5.3 μm wide. Externally, the longitudinal canal is lanceolate to linear, slightly expanded in the middle of the valve with three rows of cribrate areolae (>30 poroids) narrowing into one at the valve apices ( Figs 85–98, 100 ). Internally, a thick non-porous slightly raised silica plate encloses the longitudinal canal ( Figs 102, 105, 106 ). Externally, the raphe is filiform, curved; the proximal ends are within expanded teardrop depressions ( Figs 97, 101 ). The distal raphe ends are unilaterally bent to the same side and terminate at the valve face mantle junction ( Figs 97, 98 ). 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 ( Figs 102–104 ). The striae are parallel at mid-valve becoming radiate towards the valve apices, 9–10 in 10 μm. Striae are uniseriate becoming biseriate towards the valve margins (white arrow in Fig. 99 ). The striae are composed of large round to rectangular areolae covered externally with a fine pored cribra (>40 poroids), 13–15 in 10 μm. The inter-areolar thickenings have crested fin-like ridges, which are serrated into ca. 5–7 notched edges ( Fig. 100 ). The areolae increase in size towards the valve margins ( Figs 97, 100 ). Internally, the alveoli open via a single elongated opening covered with a thin silica layer ( Fig. 107 ). The valvocopula has serrated advalvar edges ( Figs 105, 106 ).

Type:— UNITED REPUBLIC OF TANZANIA, Lake Tanganyika , Jakobsen Beach, at 783 m elevation; submerged roots, 1 m water depth, 4°54’33.4” S 29°35’54.5” E, E. Jovanovska, October 7 th 2019 (holotype designated here, circled specimen BM-108973! = Fig. 91 , isotypes ANSP-GC17202 !, CANA-129320!). Type material CANA-129320. Registration: http://phycobank.org/103722

Pictures of the isolated specimen:— LM micrograph on 1000× magnification ( Fig. S3s ).

Sequence data:— Plastid gene rbc L sequence (GenBank accession: OQ 660276).

Etymology:— The specific epithet ‘ latiuscula ’ refers to the broad width of the valves.

Ecology and distribution:— Diploneis latiuscula sp. nov. has only been observed from the type material, the northern sub-basin of Lake Tanganyika from the Tanzanian side (see Fig. 1c, d ). Since it was found on submerged roots, the community consisted mainly of epiphytic species with occasional occurrences of D. duplex sp. nov. Diploneis latiuscula sp. nov. is very rare in the type material and could therefore have been found in these roots as a result of water currents, upwelling or turbulence, considering its proximity to the sandy areas that are probably its natural living substrate.

Main differential characters:— Valve shape, striae pattern, external like-fin ornamentations across the valve, and poroids>40 per areola.

Similar species:— Diploneis tanganyikae sp. nov., D. cristata sp. nov., Diploneis tumida sp. nov., Diploneis lecohuiana Lange-Bertalot & Fuhrmann (2017: 26) , and Diploneis ellipticasinensis Lange-Bertalot & Fuhrmann (2020: 42) .

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 85–96. Diploneis latiuscula sp. nov., LM valve views, Lake Tanganyika. All specimens displayed are from the type material, Jakobsen Beach. Fig. 91. Holotype specimen. Scale bar = 10 μm.

FIGURES 97–101. Diploneis latiuscula sp. nov., SEM external valve views, Lake Tanganyika, Jakobsen Beach. 97. Whole valve. 98. Distal raphe ends with deflected terminal fissures. 99. White arrowed uniseriate becoming biseriate striae pattern. 100. Detail areolae structure and inter-areolar thickenings with serrated fin-like silica ridges. 101. Central area with recessed proximal raphe ends. Scale bars = 10 μm (Fig. 97), 2 μm (Figs 98, 100, 101), 1 μm (Fig. 99).

FIGURES 102–107. Diploneis latiuscula sp. nov., SEM internal valve views, Lake Tanganyika, Jakobsen Beach. 102, 105, 106. View of a whole valve, showing raphe structure and alveoli structure. 103. Detail of mid-valve, showing simple and slightly elevated proximal raphe ends. 104. Distal raphe ends simple and slightly elevated. 107. Close view of the alveoli opening covered by a thin silica layer. Scale bars = 10 μm (Fig. 105), 5 μm (Figs 102, 106), 2 μm (Figs 103, 104, 107).

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.