Diploneis lunata, 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 : 43

Diploneis lunata sp. nov. (LM Figs 193–205 , SEM Figs 206–213 )

Valves are weakly asymmetric, linear-elliptic with parallel to weakly convex margins and round apices ( Figs 193–206 ). Valve length is 26.5–55 μm and valve width is 16–25 μm. The axial area is narrow, lanceolate, slightly expanding into a longitudinally elongate and weakly asymmetric central area ( Figs 195 , 206, 207 ), 2.8–4 μm wide. Externally, the canal is lanceolate, slightly expanded in the middle of the valve with three rows of large cribrate (ca. 10 poroids) areolae narrowing into two to one at the valve apices ( Figs 193–208 ). Internally, a thick non-porous slightly raised silica plate encloses the longitudinal canal ( Fig. 210 ). Externally, the raphe is filiform, curved with deflected teardrop proximal ends; the raphe ends are positioned within an elongated teardrop depression ( Figs 206, 207 ). The distal raphe ends are unilaterally bent to the same side and terminate on the valve face ( Figs 206, 208 ). Internally, the raphe is curved with simple proximal and distal ends that are slightly elevated in a depression formed by the longitudinal canal ( Figs 210– 212 ). The striae are parallel at mid-valve changing to radiate towards the apices, 9–10 in 10 μm. Striae are uniseriate becoming biseriate towards the valve margins ( Figs 206, 209 ). The striae are composed of round to rectangular areolae covered externally with cribra (15–25 poroids), 12–15 in 10 μm. The inter-areolar thickenings have transapical and longitudinal fin-like silica ridges serrated with ca. 5–8 notched edges. The canal ridges are slightly bent into a semi-circular shape. The areolae increase in size towards the valve margins ( Figs 206, 208 ). Internally, the alveoli open via a single elongated opening covered with a thin silica layer ( Fig. 213 ).

Type:— UNITED REPUBLIC OF TANZANIA, Lake Tanganyika , Kiganza Bay near Gombe National Park, at 768 m elevation; sand, 12 m water depth, collected SCUBA diving, 4°47’44.9” S 29°35’57.6” E, A. Indermaur, 8 th July 2019 (holotype designated here, circled specimen BM-108988! = Fig. 197 , isotypes ANSP-GC17217 !, CANA-129319!). Type material CANA-129319. Registration: http://phycobank.org/103713

Pictures of the isolated specimen:— LM micrograph on 1000× magnification ( Fig. S2i ).

Sequence data:— Plastid gene rbc L sequence (GenBank accession: OQ 660292).

Etymology:— The specific epithet ‘ lunata ’ refers to the crescent-shaped fin-like silica ridges in the canal region of the valve face.

Ecology and distribution:— This species has only been observed along the Tanzanian coast of Lake Tanganyika. It is a very rare species in a few very narrow areas in the central and northern basins of the lake, mainly in Kiganza Bay and less so in Kalya Bay, Mahale National Park, and the Rukoma area ( Fig. 1c–e ). In the alkaline, moderately mineral-rich and highly transparent waters, it was found on the sandy stretches between 12 and 33 m water depth, but also on submerged rocks at Jakobsen Beach, where it was probably brought by water currents or turbidity. Diploneis lunata sp. nov. usually occurs together with D. kilhamiana sp. nov., D. cocquytiana sp. nov., D. tanganyikae sp. nov., and D. serrulata sp. nov.

Main differential characters:— Valve shape, striae pattern, striae density, external fin-like ornamentations across the valve, broad virgae, and poroids 15–25 per areola.

Similar species:— Diploneis fossa sp. nov., Diploneis parahinziae Lange-Bertalot, Fuhrmann & Ringel (in Lange-Bertalot & Fuhrmann 2016: 168), and Diploneis heisingeriae Jurilj (1954: 127) .

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 193–205. Diploneis lunata sp. nov., LM valve views, Lake Tanganyika. 193. Specimen from Kalya Bay. 194, 196. Specimens from Mahale National Park. 195, 197, 199–205. Specimens from Kiganza Bay. 198. Specimen from Jakobsen Beach. Fig. 197. Holotype specimen. Scale bar = 10 μm.

FIGURES 206–213. Diploneis lunata sp. nov., SEM external (Figs 206–209) and internal (Figs 210–213) valve views, Lake Tanganyika, Kiganza Bay. 206. View of a whole valve. 207. Central area with teardrop shaped proximal raphe ends. 208. Distal raphe ends with deflected terminal fissures. 209. Broken valve, showing the chambered wall structure. 210. View of a whole valve. 211. Central area with simple and slightly elevated proximal raphe ends. 212. Distal raphe endings slightly elevated and distant from the valve apices. 213. Detail alveoli openings covered by thin silica layers. Scale bars = 5 μm (Figs 206, 210), 2 μm (Figs 209, 211), 1 μm (Figs 207, 208, 212, 213).

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.