Diploneis elongata, 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 : 71

Diploneis elongata sp. nov. (LM Figs 442–456 , SEM Figs 457–461 )

Valves are weakly asymmetric, elliptical to linear–elliptical with parallel margins and bluntly round apices ( Figs 442– 457 ). The length of the valve is 30–50 μm and the width is 17–20 μm. The axial area is narrow, lanceolate, widening at the center to form a longitudinally elongate and weakly asymmetric central area ( Figs 442 , 457, 458 ), 3.4–4.4 μm wide. Externally, the longitudinal canal is lanceolate, slightly expanded in the middle of the valve with three rows of large cribrate (5–7 poroids) areolae narrowing into one at the valve apices ( Figs 443 , 457, 458, 460 ). Externally, the raphe is filiform, curved with straight to weakly deflected proximal ends lying within linearly expanded teardrop depressions ( Figs 457, 458 ). The distal raphe ends are unilaterally bent to the same side as the proximal ends and terminate on the valve face ( Figs 457, 461 ). The striae are parallel at mid-valve becoming radiate towards the valve apices, 9–10(11) in 10 μm. Striae are biseriate throughout (white arrow in Fig. 458 ). The striae are composed of round areolae covered externally with cribra (8–15 poroids), 15–18 in 10 μm. The inter-areolar thickenings have fin-like silica ridges serrated with ca. 6 notched edges ( Fig. 459 ). The fin-like ornamentations are evenly distributed across the valve and on the canal are bent into semi-circular shapes, positioned towards the striae whereas those of the striae are only slightly bent towards the canal, changing opposite direction only at valve mantle ( Figs 457, 458, 461 ). The areolae increase in size towards the valve margins ( Figs 458, 459 ).

Type:— REPUBLIC OF ZAMBIA, Lake Tanganyika , Kalambo Falls Lodge, at 784 m elevation; sand from fish crater, 7.5 m water depth, collected SCUBA diving, 8°37’22.9” S 31°12’01.8” E, W. Salzburger, 29 th September 2021 (holotype designated here, circled specimen BM-108980! = Fig. 456 , isotypes ANSP-GC17209 !, CANA-129325!). Type material CANA-129325. Registration: http://phycobank.org/103707

Pictures of the isolated specimen:— LM micrograph on 1000× magnification ( Fig. S3o ).

Sequence data:— Plastid gene rbc L sequence (GenBank accession: OQ 660287).

Etymology:— The specific epithet ‘ elongata ’ refers to the elongated shape of the valves.

Ecology and distribution:— Diploneis elongata sp. nov. has been observed in Lake Tanganyika in the three sub-basins on the Zambian and Tanzanian side. In the alkaline, moderately mineral-rich and highly transparent waters, the species occurs in relatively large numbers on mud and sand as well as on sand fish craters between 8 and 33 m water depth, especially at Kalambo Falls Lodge, Isanga Bay, Cape Nangu in Kasaba Bay, Mahale National Park, and Kiganza Bay (see Fig. 1c–f ). At all sites D. elongata sp. nov. usually occurs together with D. fossa sp. nov., D. serrulata sp. nov., D. kilhamiana sp. nov., D. cocquytiana sp. nov., D. cristata sp. nov., D. clara sp. nov., D. salzburgeri sp. nov., and D. gigantea sp. nov.

Main differential characters:— Valve shape, striae pattern, narrow canals, external fin-like ornamentations across the valve, and poroids <15 per areola.

Similar species:— Diploneis cocquytiana sp. nov. and Diploneis hinziae Lange-Bertalot & Fuhrmann (2016: 163) .

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 442–456. Diploneis elongata sp. nov., LM valve views, Lake Tanganyika. 442. Specimen from Kasaba Bay. 443–446, 449– 452, 454–456. Specimens from Kalambo Falls Lodge. 447, 448, 453. Specimens from Kiganza Bay. Fig. 456. Holotype specimen. Scale bar = 10 μm.

FIGURES 457–461. Diploneis elongata sp. nov., SEM external valve views, Lake Tanganyika. 457, 458. Specimen from Kiganza Bay. 459, 460. Specimen from Jakobsen Beach. 461. Specimen from Kalambo Falls Lodge. 457, 460. View of a whole valve. 458. Central area showing the teardrop shaped depression with proximal raphe ends; note inter-areolar semi-circular shaped fin ornamentations of the canal and biseriate striae (white arrow). 459. Close view of the areolae structure in a broken specimen. 461. Distal raphe ends with deflected terminal fissures. Scale bars = 10 μm (Figs 457, 460), 5 μm (Fig. 458), 2 μm (Figs 459, 461).

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.