Diploneis tenera, 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 : 37

Diploneis tenera sp. nov. (LM Figs 152–171 , SEM Figs 172–177 )

Valves are asymmetric, linear-elliptic with parallel to weakly convex margins and round apices ( Figs 152–172 ). Valve length is 29–47.5 μm and valve width is 14.5–20 μm. The axial area is linear to lanceolate, widening at the center to form a longitudinally elongate and weakly asymmetric central area ( Figs 153 , 172 ), 2.5–4 μm wide. Externally, the canal is linear to lanceolate, slightly expanded in the middle of the valve with three rows of cribrate areolae narrowing into one at the valve apices ( Figs 152–172 ). Internally, a thick non-porous slightly raised silica plate encloses the longitudinal canal ( Fig. 174 ). Externally, the raphe is filiform, curved with expanded proximal ends deflected to one side; the proximal ends are positioned within tear drop depressions ( Fig. 172 ). The distal raphe ends are unilaterally bent to the same side and terminate at the valve face mantle junction ( Figs 172, 173 ). Internally, the raphe is curved with simple proximal and distal ends that are slightly elevated in a depression formed by the longitudinal canal ( Figs 174, 175, 177 ). The striae are parallel at mid-valve changing to radiate towards the valve apices, 10–11 in 10 μm. Striae are uniseriate becoming biseriate towards the valve margins ( Figs 173, 175 ). The striae are composed of round to rectangular areolae covered externally with a dense cribra (>15 poroids), 15–20 in 10 μm. The inter-areolar thickenings have fin-like crest shaped silica ornamentations serrated into ca. 3–5 notched edges ( Fig. 173 ). The fin-like ornamentations around the canal are bent into semi-circular shapes, positioned towards the striae whereas those of the striae are only slightly bent and positioned towards the canal, changing opposite direction only at valve mantle ( Figs 172, 173 ). The areolae increase in size towards the valve margins ( Fig. 173 ). Internally, the alveoli open via a single elongated opening covered with a thin silica layer ( Fig. 176 ). The valvocopula has serrated advalvar edges ( Figs 174, 176 ).

Type:— REPUBLIC OF ZAMBIA, Lake Tanganyika , Kalambo Falls Lodge, at 782 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-108981! = Fig. 157 , isotypes ANSP-GC17210 !, CANA-130009!). Type material CANA-129325. Registration: http://phycobank.org/103719

Pictures of the isolated specimen:— LM micrograph on 1000× magnification ( Fig. S3q ).

Sequence data:— Plastid gene rbc L sequence (GenBank accession: OQ 660297).

Etymology:— The specific epithet ‘ tenera ’ refers to structurally simple valves and valve ornamentations.

Ecology and distribution:— Diploneis tenera sp. nov. has only been observed along the Zambian and Tanzanian coasts of Lake Tanganyika. In the alkaline, moderately mineral-rich and highly transparent waters, the species occurs mainly in sandy substrates (sometimes with mollusk shells) and rarely in submerged rocks between 15 and 20 m water depth in the southern sub-basin at Kalambo Falls Lodge, Isanga Bay, Mutondwe Island, and Cape Nangu in Kasaba Bay, and less so in the central sub-basin in Mahale National Park (see Fig. 1c, e, f ). It is quite abundant especially at Kalambo Falls Lodge and in Kasaba Bay where it occurs together with D. kilhamiana sp. nov., D. gigantea sp. nov., D. decora sp. nov., D. serrulata sp. nov., D. salzburgeri sp. nov., D. duplex sp. nov., and D. clara sp. nov.

Main differential characters:— Valve shape, striae pattern, external thick fin-like ornamentations across the valve, and poroids 15–20 per areola.

Similar species:— Diploneis tessellata sp. nov. and Diploneis rumrichorum Lange-Bertalot & Fuhrmann (2020: 121) .

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 152–171. Diploneis tenera sp. nov., LM valve views, Lake Tanganyika. 152, 154. Specimens from Isanga Bay. 153, 171. Specimens from Mahale National Park. 155–165, 167–169. Specimens from Kalambo Falls Lodge. 166, 170. Specimens from Kasaba Bay. Fig. 157. Holotype specimen. Scale bar = 10 μm.

FIGURES 172–177. Diploneis tenera sp. nov., SEM external (Figs 172, 173) and internal (Figs 174–177) valve views, Lake Tanganyika. 172, 173. Specimen from Isanga Bay. 174–177. Specimen from Kalambo Falls Lodge. 172. A whole valve, showing raphe structure and inter-areolar thickenings with serrated fin-like silica ridges. 173. Close view of areolae structure and distal raphe ends with deflected terminal fissures. 174. View of a corroded valve, showing raphe structure, alveoli structure, and valvocopula with serrated advalvar edges. 175. Detail mid-valve, showing simple and slightly elevated proximal raphe ends. 176. Alveoli with corroded thin silica layers showing uniseriate becoming biseriate striae; valvocopula with serrated edge. 177. Distal raphe ends simple and slightly elevated. Scale bars = 10 μm (Fig. 172), 5 μm (Fig. 174), 2 μm (Figs 173, 175), 1 μm (Figs 176, 177).

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.