Diploneis cristata, 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 : 16

Diploneis cristata sp. nov. (LM Figs 47–52 , SEM Figs 53–60 )

Valves are weakly asymmetric, rhombic-elliptic to elliptic with convex margins and bluntly round apices ( Figs 47–53 ). Valve length is 47–80.5 μm and valve width is 26–41 μm. The axial area is narrow, lanceolate, widening at the center to form a lanceolate central area ( Figs 47 , 55 ), 4.5–8.5 μm wide. Externally, the longitudinal canal is broad, lanceolate to linear, slightly expanded in the middle of the valve with three to four rows of cribrate (10–20 poroids) areolae narrowing into one at the valve apices ( Figs 53, 55, 56 ). Internally, a thick non-porous slightly raised silica plate encloses the longitudinal canal ( Figs 57, 59 ). Externally, the raphe is filiform, curved; the proximal ends are weakly deflected and positioned within a teardrop depression ( Figs 53, 55 ). The distal raphe ends are unilaterally bent to the same side and terminate on the valve face ( Figs 53, 56 ). Internally, the raphe branches are slightly arched with simple proximal and distal ends that are slightly elevated in a deep depression formed by the longitudinal canal ( Fig. 57 ). The striae are parallel at mid-valve becoming radiate towards the valve apices, 7–8 in 10 μm. Striae are uniseriate throughout ( Fig. 54 ). The striae are composed of large round to rectangular areolae covered externally with cribra (>40 poroids; hardly visible on the illustrated specimens), 7–8 in 10 μm. Each areola opens into deep pits and sometimes separated by short crested fin-like ridge ornamentations that are forming from the areolae wall (white arrowed Fig. 54 ). The inter-areolar thickenings have fin-like shaped silica ornamentations serrated into ca. 3–9 notched edges ( Figs 54, 56 ). The areolae increase in size towards the valve margins ( Figs 53, 55 ). Internally, the alveoli open via a single elongated opening covered with a thin silica layer ( Figs 59, 60 ). The valvocopula has serrated advalvar edges ( Figs 57, 59, 60 ).

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-108995! = Fig. 48 , isotypes ANSP-GC17224 !, CANA-129321!). Type material CANA-129321. Registration: http://phycobank.org/103701

Pictures of the isolated specimen:— LM micrograph on 1000× magnification ( Fig. S2e ).

Sequence data:— Plastid gene rbc L sequence (GenBank accession: OQ 660279).

Etymology:— The specific epithet ‘ cristata ’ is derived from the distinct crested fin-like ridge ornamentations on the valve face.

Ecology and distribution:— Diploneis cristata sp. nov. has been observed along the Tanzanian and Zambian coasts of Lake Tanganyika. It is not a very frequent species in this alkaline lake with moderate mineral content, occurring mainly on muddy and sandy substrates between 5 and 25 m water depth, but also as tychoplankton in the littoral areas and in plankton up to 60 m depth. This species occurs mainly in the southern sub-basin at Kalambo Falls Lodge, Isanga Bay, Chituta Bay, Mutondwe Island, and Ndole Bay ( Fig. 1c, f ). In this sub-basin, the species occurs mainly together with D. gigantea sp. nov., D. fossa sp. nov., D. cocquytiana sp. nov., and D. salzburgeri sp. nov. Smaller population sizes of this species have been observed in the central and northern sub-basins in Kalya Bay, Mahale National Park, Rukoma area, Buhingu Island, and Kiganza Bay ( Fig. 1c–e ). In these areas, the species usually coexists with D. serrulata sp. nov., D. cocquytiana sp. nov., D. lunata sp. nov., D. salzburgeri sp. nov., and D. tanganyikae sp. nov.

Main differential characters:— Valve size and shape, striae density, external thick fin-like ornamentations across the valve, fin-like thickening within areolae, and poroids>40 per areola.

Similar species:— Diploneis tanganyikae sp. nov., D. salzburgeri sp. nov., and Diploneis buriatica Kulikovskiy & Lange-Bertalot (2015: 91) .

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 47–52. Diploneis cristata sp. nov., LM valve views, Lake Tanganyika. 47, 49–52. Specimens from Kalambo Falls Lodge. 48. Specimen from Chituta Bay. Fig. 48. Holotype specimen. Scale bar = 10 μm.

FIGURES 53–56. Diploneis cristata sp. nov., SEM external valve views, Lake Tanganyika. 53, 55. Specimen from Isanga Bay. 54, 56. Specimen from Ndole Bay. 53. Whole valve. 54. Close view of striae structure; arrowed areola divided by thick thickenings bearing fin-like silica ridges. 55. Central area with extended teardrop shaped depressions with proximal raphe ends. 56. Distal raphe ends with deflected terminal fissures. Scale bars = 10 μm (Fig. 53), 5 μm (Figs 55, 56), 2 μm (Fig. 54).

FIGURES 57–60. Diploneis cristata sp. nov., SEM internal valve views, Lake Tanganyika, Isanga Bay. 57. Whole valve. 58. Central area with simple and slightly elevated proximal raphe ends. 59. Mid-valve, showing proximal raphe ends and alveolate openings covered by a thin silica layer. 60. Close view of alveoli and valvocopula with serrated advalvar edges. Scale bars = 10 μm (Fig. 57), 5 μm (Figs 58–60).

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.