Diploneis cocquytiana, 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 : 67

Diploneis cocquytiana sp. nov. (LM Figs 419–433 , SEM Figs 434–441 )

Valves are weakly asymmetric, linear-elliptic with parallel to weakly convex margins and round apices ( Figs 419– 434 ). Valve length is 35.5–62 μm and width is 15–20 μm. The axial area is narrow, lanceolate, slightly expanding into a small to indistinguishable central area ( Figs 420 , 434, 435 ), 3–4.8 μm wide. Externally, the canal is broad, linear to lanceolate, slightly expanded in the middle of the valve with four rows of cribrate (ca. 10 poroids) areolae narrowing into one at the valve apices ( Figs 420 , 434, 435, 437 ). Internally, a thick non-porous slightly raised silica plate encloses the longitudinal canal ( Fig. 439 ). Externally, the raphe is filiform, curved with simple deflected proximal ends; linear expanded lanceolate depressions hold the proximal ends ( Figs 435, 437 ). The distal raphe ends are unilaterally bent to the same side and terminate on the valve face at the mantle ( Figs 434, 436, 438 ). Internally, the raphe is curved with simple proximal and distal ends that are slightly elevated with a small helictoglossa, and positioned in a depression formed by the longitudinal canal ( Figs 439–441 ). The striae are parallel at mid-valve becoming radiate towards the apices, 9–10(11) in 10 μm. Striae are uniseriate becoming biseriate towards the valve margins (white arrow in Fig. 438 ). The striae are composed of round to rectangular areolae covered externally with fine pored cribra (20–30 poroids), 15–20 in 10 μm. The inter-areolar thickenings have fin-like silica ridges serrated with ca. 5–8 notched edges. The areolae increase in size towards the valve margins ( Figs 435, 438 ). Internally, the alveoli open via a single elongated opening covered with a thin silica layer ( Figs 439, 440 ).

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 108984 ! = Fig. 429 , isotypes ANSP-GC17213 !, CANA-129315!). Type material CANA-129315. Registration: http://phycobank.org/103700

Pictures of the isolated specimen:— LM micrograph on 1000× magnification ( Fig. S2j ).

Sequence data:— Plastid gene rbc L sequence (GenBank accession: OQ 660288).

Etymology:— The specific epithet ‘ cocquytiana ’ honors Dr. Christine Cocquyt, who has made many significant contributions to diatom research from materials collected from Lake Tanganyika.

Ecology and distribution:— This species has been observed in Lake Tanganyika in the three sub-basins on the shores of Zambia and Tanzania (including the coast of Burundi; Cocquyt 1998, fig. 14: 4). The species is very abundant in the alkaline, moderately mineral-rich and very transparent lake, where it occurs on sandy and muddy substrates (sometimes with mollusk shells) between 5 and 36 m water depth. It can also be found in submerged rocks in the littoral areas at Jakobsen Beach or to a water depth of 3 m in Chituta Bay and free-living (i.e. tychoplanktonic) in plankton to a depth of 60 m in Mahale National Park, probably resulting from water currents and turbulence. Diploneis cocquytiana sp. nov. mostly coexists with D. fossa sp. nov., D. serrulata sp. nov., D. kilhamiana sp. nov., D. angusta sp. nov., D. cristata sp. nov., D. salzburgeri sp. nov., and D. tanganyikae sp. nov. in Kalambo Falls Lodge with well-established populations as well as in Mahale National Park, Cape Nangu at Kasaba Bay, Ndole Bay, Kiganza Bay, Chituta Bay, Mutondwe Island, and the Rukoma area (see Fig. 1c–f ).

Main differential characters:— Valve shape, canal width, striae pattern, external fin-like ornamentations across the valve, fins scattered over the canals, and poroids <30 per areola.

Similar species:— Diploneis elongata sp. nov., Diploneis fontium Reichardt & Lange-Bertalot (2004: 433) , and Diploneis mollenhaueri Lange-Bertalot & Fuhrmann (2020: 85) .

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 419–433. Diploneis cocquytiana sp. nov., LM valve views, Lake Tanganyika. 419, 420, 422, 423–426, 428, 429, 431, 432. Specimens from Kalambo Falls Lodge. 421, 427, 430. Specimens from Kiganza Bay. 433. Specimen from Rukoma area. Fig. 429. Holotype specimen. Scale bar = 10 μm.

FIGURES 434–438. Diploneis cocquytiana sp. nov., SEM external valve views, Lake Tanganyika, Isanga Bay. 434, 437. View of a whole valve. 435. Mid-valve, showing linear extended teardrop shaped depressions with proximal raphe ends and serrated inter-areolar fin-like shaped ornamentations. 436. Half-valve, showing the raphe branch system. 438. Distal raphe end with deflected terminal fissure; white arrowed uniseriate becoming biseriate striae pattern. Scale bars = 10 μm (Figs 434, 437), 5 μm (Figs 435, 436, 438).

FIGURES 439–441. Diploneis cocquytiana sp. nov., SEM internal valve views, Lake Tanganyika, Mutondwe Island. 439.A whole valve. 440. Detail valve apices, showing simple and slightly elevated distal raphe ends and openings of the alveoli covered by thin silica layer. 441. Central area with simple and slightly elevated proximal raphe ends. Scale bars = 10 μm (Fig. 439), 5 μm (Figs 440, 441).

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.