Diploneis tessellata, 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 : 33

Diploneis tessellata sp. nov. (LM Figs 132–141 , SEM Figs 142–151 )

Valves are weakly asymmetric, broadly elliptic with convex margins and bluntly round ends ( Figs 132–143 ). Valve length is 29.5–60.5 μm and valve width is 18.5–33.5 μm. The axial area is narrow, lanceolate, widening at the center to form an elongate and weakly asymmetric central area ( Figs 133 , 145, 146 ), 3.5–6.5 μm wide. Externally, the canal is linear to lanceolate, slightly expanded in the middle of the valve with three rows of cribrate (<9 poroids) areolae narrowing into one at the valve apices ( Figs 132–141 , 146, 147 ). Internally, a thick non-porous slightly raised silica plate encloses the longitudinal canal ( Figs 148–151 ). Externally, the raphe is filiform, curved with simple proximal ends deflected to one side; the proximal raphe ends are positioned within expanded teardrop depressions ( Figs 145, 146 ). The distal raphe ends are unilaterally bent to the same side and terminate at the valve face mantle junction ( Figs 142, 144 ). Internally, the raphe is curved with simple proximal and distal ends that are slightly elevated in a depression formed by the longitudinal canal ( Figs 148–151 ). The striae are parallel at mid-valve becoming radiate towards the valve apices, 8–9 (mostly 8) in 10 μm. Striae are uniseriate throughout (white arrow in Fig. 142 ). The striae are composed of round to rectangular areolae covered externally with fine pored cribra (25–45 poroids), 8–10 in 10 μm. The inter-areolar thickenings have fin-like silica ridges that are serrated with ca. 5–7 notched edges ( Fig. 146 ). The areolae increase in size towards the valve margins ( Figs 142, 143, 147 ). Internally, the alveoli open via a single elongated opening covered with a thin silica layer ( Figs 148, 149 ). The valvocopula has serrated advalvar edges ( Figs 148, 150 ).

Type:— REPUBLIC OF ZAMBIA, Lake Tanganyika , Kalambo Falls Lodge, at 770 m elevation; mud, 18 m water depth, collected SCUBA diving, 8°37’25.6” S 31°11’59.7” E, H. Büscher, 1 st September 2018 (holotype designated here, circled specimen BM-108986! = Fig. 138 , isotypes ANSP-GC17215 !, CANA-129336!). Type material CANA-129315. Registration: http://phycobank.org/103720

Pictures of the isolated specimen:— LM micrograph on 1000× magnification ( Fig. S 3t ).

Sequence data:— Plastid gene rbc L sequence (GenBank accession: OQ 660296) and nuclear encoded 18S ( SSU rDNA) sequence (GenBank accession: OQ 629557).

Etymology:— The specific epithet ‘ tessellata ’ refers to the blocky, tiled appearance of the areolae of this species.

Ecology and distribution:— This species has only been observed in Lake Tanganyika along the coasts of Zambia and Tanzania in the three sub-basins, especially in Kalambo Falls Lodge, Isanga Bay, Mutondwe Island, Kalya Bay, Rukoma area, and Kiganza Bay (see Fig. 1c–f ). The species is not very abundant in the alkaline, moderately mineral-rich and highly transparent waters and occurs in sandy and muddy substrates (sometimes with mollusk shells) between 10 and 33 m water depth. It can also be found on submerged rocks in the littoral areas at Jakobsen Beach, at 5 m depth on Buhingu Island, and at 20 m depth in Isanga Bay, probably due to upwelling, currents, and/or turbidity. Diploneis tessellata sp. nov. occurs together with D. salzburgeri sp. nov., D. cristata sp. nov., D. gigantea sp. nov., D. fossa sp. nov., D. cocquytiana sp. nov., D. kilhamiana sp. nov., D. tanganyikae sp. nov., and D. serrulata sp. nov.

Main differential characters:— Valve shape, striae density, areolae density, external thick fin-like ornamentations evenly distributed across the valve, and poroids 25–45 per areola.

Similar species:— Diploneis tenera sp. nov., D. cristata sp. nov., and D. elliptica .

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 132–141. Diploneis tessellata sp. nov., LM valve views, Lake Tanganyika. 132, 134–141. Specimens from Kalambo Falls Lodge. 133. Specimen from Kalya Bay. Fig. 138. Holotype specimen. Scale bar = 10 μm.

FIGURES 142–147. Diploneis tessellata sp. nov., SEM external valve views, Lake Tanganyika. 142, 144, 145. Specimen from Kiganza Bay. 143, 146, 147. Specimens from Isanga Bay. 142, 143. View of a whole valve; white arrowed uniseriate striae pattern. 144. Distal raphe ends with deflected terminal fissures. 145. Detail semi-circular shaped interalveolar fin ornamentations on the canal. 146. Central area with bent teardrop depression with proximal raphe ends. 147. Half-valve showing the raphe branch. Scale bars = 10 μm (Fig. 143), 5 μm (Figs 142, 147), 2 μm (Figs 144–146).

FIGURES 148–151. Diploneis tessellata sp. nov., SEM internal valve views, Lake Tanganyika. 148. Specimen from Mutondwe Island. 149. Specimen from Kalambo Falls Lodge. 150. Specimen from Isanga Bay. 151. Specimen from Rukoma area. 148–151. View of a whole valve, showing simple and slightly elevated raphe, alveoli covered by a thin silica layer, and closed longitudinal canal. Scale bar = 10 μm.

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.