Diploneis kilhamiana, 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 : 59

Diploneis kilhamiana sp. nov. (LM Figs 349–372 , SEM Figs 373–383 )

Valves are weakly asymmetric, linear-elliptic with parallel to weakly convex margins and round apices ( Figs 349–373 ). Valve length is 22.5–43 μm and width is 11.5–15 μm. The axial area is linear to lanceolate, widening at the center to form a small lanceolate central area ( Figs 351 , 373, 376 ), 2.5–3.5 μm wide. Externally, the canal is linear to lanceolate, slightly expanded in the middle of the valve with two rows of cribrate (8–15 poroids) areolae narrowing into one at the valve apices ( Figs 351 , 373, 375 ). Internally, a thick non-porous slightly raised silica plate encloses the longitudinal canal ( Figs 379, 381 ). Externally, the raphe is filiform, curved with expanded proximal ends weakly deflected to one side; the proximal ends are positioned within an elongated teardrop depression ( Figs 373, 375, 376 ). The distal raphe ends are unilaterally bent to the same side and terminate as expanded pores at the valve face margin ( Figs 374, 375, 377 ). Internally, the raphe is curved with simple proximal and distal ends that are slightly elevated in a depression formed by the longitudinal canal ( Figs 380, 381, 383 ). The striae are parallel at mid-valve becoming radiate towards the apices, 9–11 in 10 μm. Striae are biseriate throughout ( Figs 378 , 379, 382 ). The striae are composed of round to rectangular areolae covered externally with fine pored cribra (15–20 poroids), 20 in 10 μm. The inter-areolar thickenings have fin-like silica ridges serrated with ca. 8–10 notched edges ( Fig. 374 ). The fin-like silica ornamentations along the canal are slightly bent into a semi-circular shape, positioned towards the striae whereas those of the striae are only slightly bent towards the canal and change direction only at the valve mantle ( Figs 374–376 ). The areolae increase in size towards the valve margins ( Fig. 378 ). Internally, the alveoli open via a single elongated opening covered with a thin silica layer ( Figs 380–382 ). The valvocopula has serrated advalvar edges ( Figs 379–382 ).

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-108985! = Fig. 370 , isotypes ANSP-GC17214 !, CANA-129335!). Type material CANA-129315. Registration: http://phycobank.org/103710

Pictures of the isolated specimen:— LM micrograph on 1000× magnification ( Fig. S3v ).

Sequence data:— Plastid gene rbc L sequence (GenBank accession: OQ 660280).

Etymology:— The specific epithet ‘ kilhamiana ’ honors Dr. Susan S. Kilham, who made many contributions to the field of diatom ecology, including research in Lake Tanganyika.

Ecology and distribution:— This species has been observed in Lake Tanganyika, where the water is predominantly alkaline, moderately mineral-rich and very transparent. The species is widespread in the southern, central, and northern sub-basins on the Tanzanian and Zambian sides (including Burundi, see Cocquyt 1999, fig. 16), especially at Kalambo Falls Lodge, Cape Nangu in Kasaba Bay, Mahale National Park, Kiganza Bay, as well as Isanga Bay, Chituta Bay, and the Rukoma area (see Fig. 1c–f ). Diploneis kilhamiana sp. nov. inhabits sandy and muddy substrates (sometimes with mollusk shells) between 10 and 36 m water depth. A few specimens were found in 70 m water depth in the cleaned samples from Chituta Bay, and live specimens were found on the submerged rocks in the coastal areas at Jakobsen Beach near Kigoma, probably due to sediment distribution caused by currents and water turbulence at both sites. This species normally coexists with D. cocquytiana sp. nov., D. gigantea sp. nov., D. salzburgeri sp. nov., D. tenera sp. nov., D. nana sp. nov., D. fossa sp. nov., D. angusta sp. nov., and D. cristata sp. nov.

Main differential characters:— Valve shape, striae pattern, and external thick fin-like ornamentations across the valve; fins more randomly distributed across the canals.

Similar species:— Diploneis cocquytiana sp. nov., Diploneis heteromorphiforma Metzeltin, Lange-Bertalot & Nergui (2009: 35) , and Diploneis pseudovalis Hustedt (1930: 253) .

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 349–372. Diploneis kilhamiana sp. nov., LM valve views, Lake Tanganyika. 349. Specimen from Jakobsen Beach. 350–352, 354. Specimens from Kiganza Bay. 353. Specimen from Rukoma area. 355. Specimen from Isanga Bay. 356–367, 369–372. Specimens from Kalambo Falls Lodge. 368. Specimen from Mahale National Park. Fig. 370. Holotype specimen. Scale bar = 10 μm.

FIGURES 373–378. Diploneis kilhamiana sp. nov., SEM external valve views, Lake Tanganyika. 373–376. Specimens from Kalambo Falls Lodge. 377, 378. Specimen from Isanga Bay. 373. View of a whole valve. 374. Detail valve apices, showing distal raphe ends with deflected terminal fissures and internal alveoli structure. 375. Internal and external valve view. 376. Central area with linear extended teardrop shaped depressions with proximal raphe ends and inter-areolar semi-circular shaped fin ornamentations on the canal. 377. Close view of distal raphe ends. 378. Close view of biseriate striae pattern. Scale bars = 10 μm (Fig. 373), 5 μm (Fig. 375), 2 μm (Figs 374, 376–378).

FIGURES 379–383. Diploneis kilhamiana sp. nov., SEM internal valve views, Lake Tanganyika, Rukoma area. 379.A whole valve. 380. Distal raphe endings slightly elevated and distant from the valve apices. 381. Half valve, showing raphe branch and valvocopula with serrated advalvar edges. 382. Close view of alveolate openings covered by thin silica layers; where destroyed the areolae are visible. 383. Central area with simple and slightly elevated proximal raphe ends. Scale bars = 5 μm (Fig. 379), 2 μm (Figs 380–383).

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.