Diploneis clara, 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 : 63

Diploneis clara sp. nov. (LM Figs 384–408 , SEM Figs 409–418 )

Valves are weakly asymmetric, linear-elliptic with slightly convex margins and round ends ( Figs 384–409 ). Valve length is 17.5–43.5 μm and width is 9.5–16 μm. The axial area is linear to lanceolate, widening at the center to form a longitudinally elongate and weakly asymmetric central area ( Figs 386 , 409, 411 ), 2–3.5 μm wide. Externally, the canal is linear to lanceolate, slightly expanded in the middle of the valve with two rows of cribrate (ca. 15 poroids) areolae narrowing into one at the valve apices ( Figs 386 , 409–411, 413 ). Internally, a thick non-porous slightly raised silica plate encloses the longitudinal canal ( Figs 415, 418 ). Externally, the raphe is filiform, curved with simple and deflected proximal ends; a linear expanded teardrop depression contains the proximal ends ( Figs 409, 411, 412 ). The distal raphe ends are unilaterally bent to the same side as the proximal ends, terminating on the valve face at apex margin ( Figs 409, 410, 413, 414 ). Internally, the raphe is present in a depression formed by the longitudinal canal; the raphe is curved with simple proximal and distal ends that are slightly elevated in helictoglossae ( Figs 415, 418 ). The striae are parallel at mid-valve becoming radiate towards the apices, 10–12 in 10 μm. Striae are uniseriate becoming biseriate towards the valve margins (white arrow in Figs 410 , 417 ; Figs 409, 414 ). The alveolate striae are composed of round to rectangular areolae covered externally with a pored cribra (10–15 poroids), 15–25 in 10 μm. Each areola opens into shallow pits ( Fig. 411 ). The inter-areolar thickenings have serrated fin-like silica ridges (number of notched edges hardly visible on the illustrated images). The areolae increase in size towards the valve margins ( Figs 409, 413 ). Internally, the alveoli open via a single elongated opening covered with a thin silica layer ( Fig. 416 ). The valvocopula has serrated advalvar edges ( Figs 415, 416 ).

Type:— REPUBLIC OF ZAMBIA, Lake Tanganyika , Chituta Bay, at 768 m elevation; mud and mussels, 33 m water depth, collected SCUBA diving, 8°42’56.0” S 31°09’15.0” E, W. Salzburger, 5 th September 2018 (holotype designated here, circled specimen BM-108991! = Fig. 399 , isotypes ANSP-GC17220 !, CANA-129333!). Type material CANA-129321. Registration: http://phycobank.org/103699

Pictures of the isolated specimen:— LM micrograph on 1000× magnification ( Fig. S3z ).

Sequence data:— Plastid gene rbc L sequence (GenBank accession: OQ 660281).

Etymology:— The specific epithet ‘ clara ’ refers to bright, radiant appearance in the light microscope.

Ecology and distribution:— Diploneis clara sp. nov. has only been observed in Lake Tanganyika in the three sub-basins on the Tanzanian and Zambian sides. The species is abundant in the alkaline, moderately mineral-rich and highly transparent lake. It is typically found on sand and mud (sometimes with shells) between 7.5 and 30 m water depth at Kalambo Falls Lodge, Isanga Bay, Chituta Bay, Mutondwe Island, Cape Nangu at Kasaba Bay, Ndole Bay, Mahale National Park, and Kiganza Bay (see Fig. 1c–f ). It has also been found on submerged rocks in the littoral areas at Jakobsen Beach near Kigoma, probably resulting from currents and water turbulence. This very common species cohabits with various Diploneis species at different sites, but mainly with D. cocquytiana sp. nov., D. serrulata sp. nov., D. kilhamiana sp. nov., D. duplex sp. nov., D. cristata sp. nov., D. salzburgeri sp. nov., and D. angusta sp. nov.

Main differential characters:— Valve shape, striae pattern, external fin-like ornamentations across the valve, fins fine at mid-valve, and poroids 10–15 per areola.

Similar species:— Diploneis angusta sp. nov. and Diploneis fontannella Lange-Bertalot in Werum & Lange-Bertalot (2004: 141).

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 384–408. Diploneis clara sp. nov., LM valve views, Lake Tanganyika. 384, 385. Specimens from Jakobsen Beach. 386, 387, 396, 407, 408. Specimens from Kalambo Falls Lodge. 388, 389, 397, 398, 400, 404. Specimens from Isanga Bay. 390, 391, 392, 393. Specimens from Mutondwe Island. 394, 395, 402, 403, 406. Specimens from Kiganza Bay. 399. Specimen from Chituta Bay. 401, 405. Specimens from Ndole Bay. Fig. 399. Holotype specimen. Scale bar = 10 μm.

FIGURES 409–414. Diploneis clara sp. nov., SEM external valve views, Lake Tanganyika. 409–411. Specimen from Isanga Bay. 412– 414. Specimen from Kalambo Falls Lodge. 409. A whole valve. 410. Distal raphe ends with deflected terminal fissures; white arrowed uniseriate becoming biseriate striae pattern. 411. Central area with linear extended teardrop shaped depressions with proximal raphe ends. 412. Central area of corroded valve.413. View of a corroded valve. 414. Valve apices of corroded specimen. Scale bars = 10 μm (Fig. 409), 5 μm (Figs 410, 411, 413, 414), 2 μm (Fig. 412).

FIGURES 415–418. Diploneis clara sp. nov., SEM internal valve views, Lake Tanganyika, Kiganza Bay. Fig. 415. Whole valve. Fig. 416. Close view of the alveoli openings covered by thin silica layers and the serrated advalvar edge of the valvocopula. Fig. 417. View of areolae without the fine silica covers; white arrowed biseriate striae pattern at the margins. Fig. 418. Corroded valve showing the alveoli structure. Scale bars = 10 μm (Figs 415, 418), 2 μm (Figs 416, 417).

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.