Diploneis disjuncta, 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 : 46

Diploneis disjuncta sp. nov. (LM Figs 214–248 , SEM Figs 249–257 )

Valves are weakly asymmetric, linear-elliptic with weakly convex margins and round apices ( Figs 214–250 ). Valve length is 17.5–32.5 μm and valve width is 9–13.5 μm. The axial area is very narrow, linear to lanceolate, slightly widening into a small to indistinguishable and weakly asymmetric central area ( Figs 214 , 250, 253 ), 1.8–3 μm wide. Externally, the canal is linear to lanceolate, slightly expanded in the middle of the valve with three to two rows of cribrate (<15 poroids) areolae narrowing into one at the valve apices ( Figs 249, 250, 251, 253 ). Internally, a thick non-porous slightly raised silica plate encloses the longitudinal canal ( Figs 254, 255 ). Externally, the raphe is filiform, curved with expanded proximal ends deflected to one side; the proximal raphe ends are positioned within a linear expanded depression ( Figs 250, 253 ). The distal raphe ends are unilaterally bent to the same side and terminate on the valve face ( Figs 249, 251 ). Internally, the raphe is curved with simple proximal and distal ends that are slightly elevated in a depression formed by the longitudinal canal ( Figs 254–257 ). The striae are parallel at mid-valve becoming radiate towards the apices, 11–12 in 10 μm. Striae are uniseriate at the center of the valve (white arrow in Fig. 250 ) and biseriate at the apices (black arrow in Fig. 250 ). The striae are composed of round areolae externally covered with fine pored cribra (25 poroids), 20 in 10 μm. The inter-areolar thickenings have fin-like silica ridges (mostly absent and hardly visible on the illustrated specimens probably as a result of corrosion, Figs 250, 253 ). The areolae increase in size towards the valve margins ( Fig. 252 ). Internally, the alveoli open via a single elongated opening covered with a thin silica layer ( Figs 254, 256, 257 ). The valvocopula has serrated advalvar edges ( Fig. 255 ).

Type:— REPUBLIC OF ZAMBIA, Lake Tanganyika , Cape Nandu, Kasaba Bay, at 768 m elevation; sand and mud, 20 m water depth, collected with Van Veen grab sampler, 8°30’18.9” S 30°38’32.3” E, E. Jovanovska, 2 nd October 2021 (holotype designated here, circled specimen BM-108992! = Fig. 224 , isotypes ANSP-GC17221 !, CANA-129326!). Type material CANA-129326. Registration: http://phycobank.org/103703

Pictures of the isolated specimen:— LM micrograph on 1000× magnification ( Fig. S3y ).

Sequence data:— Plastid gene rbc L sequence (GenBank accession: OQ 660294).

Etymology:— The specific epithet ‘ disjuncta ’ refers to the disjunct distribution of uniseriate and biseriate striae.

Ecology and distribution:— Diploneis disjuncta sp. nov. has only been observed along the Tanzanian and Zambian coasts in the southern and central sub-basins of Lake Tanganyika. This relatively small species is quite common in the alkaline, moderately mineral-rich and highly transparent waters on the sand and mud surface (sometimes interspersed with mollusk shells) between 15 and 33 m water depth, especially in Mahale National Park, but also in Isanga Bay, Chituta Bay, and Mutondwe Island ( Fig. 1 c, e, f ). At all sites, the species occurs together with D. decora sp. nov., D. serrulata sp. nov., D. kilhamiana sp. nov., D. cocquytiana sp. nov., D. duplex sp. nov., D. salzburgeri sp. nov., D. clara sp. nov., D. fossa sp. nov., and D. tanganyikae sp. nov.

Main differential characters:— Valve size, striae pattern, narrow canals, external fin-like ornamentations across the valve, and poroids ca. 25 per areola.

Similar species:— Diploneis duplex sp. nov. and Diploneis mineroviciae Lange-Bertalot, Fuhrmann & Werum (2020: 80) .

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 214–248. Diploneis disjuncta sp. nov., LM valve views, Lake Tanganyika. 214, 216–221, 223. Specimens from Isanga Bay. 215, 225, 228–235, 239–248. Specimens from Mahale National Park. 222. Specimen from Mutondwe Island. 224, 226, 227. Specimens from Kasaba Bay. 236–238. Specimens from Kalambo Falls Lodge. Fig. 224. Holotype specimen. Scale bar = 10 μm.

FIGURES 249–253. Diploneis disjuncta sp. nov., SEM external valve views, Lake Tanganyika. 249. Specimen from Kalambo Falls Lodge. 250–253. Specimen from Chituta Bay. 249. External and internal view of the whole frustule. 250. View of a whole valve, showing uniseriate striae at mid-valve (white arrow) and biseriate striae pattern at valve apices (black arrow). 251. Distal raphe ends with deflected terminal fissures. 252. Close view of cribra and areolae structure in a broken specimen. 253. Central area showing teardrop shaped depression with proximal raphe ends. Scale bars = 10 μm (Fig. 249), 5 μm (Figs 250, 253), 2 μm (Figs 251, 252).

FIGURES 254–257. Diploneis disjuncta sp. nov., SEM internal valve views, Lake Tanganyika. 254, 256, 257. Specimen from Kalambo Falls Lodge. 255. Specimen from Mutondwe Island. 254, 255. View of a whole valve, showing raphe structure, alveoli structure, and valvocopula with serrated advalvar edge. 256. Detail mid-valve, showing simple and slightly elevated proximal raphe ends and alveoli occluded by thin silica layers. 257. Half-valve, showing raphe branch and uniseriate becoming biseriate striae. Scale bars = 10 μm (Fig. 254), 5 μm (Figs 255, 257), 2 μm (Fig. 256).

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.