Diploneis decora, 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 : 74

Diploneis decora sp. nov. (LM Figs 462–471 , SEM Figs 472–474 )

Valves are weakly asymmetric, elliptic to weakly rhombic-elliptic with convex margins and bluntly round apices ( Figs 462–472 ). Valve length is 23.5–39 μm and width is 14–18 μm. The axial area is narrow, linear to lanceolate, expanding into the longitudinally elongate and weakly asymmetric ( Figs 464, 472 ), 4.2–6.5 μm wide central area. Externally, the longitudinal canal is broad, lanceolate to linear, slightly expanded in the middle of the valve with six rows of areolae narrowing into two to one at the valve apices ( Figs 472, 473 ). The areolae over the canal are covered by cribra (>20 poroids) and arranged in oblong circles (white arrow in Fig. 473 ). Externally, the raphe is filiform, curved with deflected proximal ends positioned within a linear expanding teardrop-shaped depression ( Figs 472, 473 ). The distal raphe ends are unilaterally bent to the same side as the proximal ends and terminate on the valve face at the mantle ( Figs 472, 474 ). The striae are parallel at mid-valve becoming radiate towards the valve apices, 10 in 10 μm. Striae are uniseriate throughout ( Fig. 473 ), composed of large rectangular areolae covered with cribra (>25 poroids) with a varied complex structure, 18–20 in 10 μm. The inter-areolar thickenings bear longitudinal fin-like ornamentations; small fin-like ridges can be present within the cribra. The areolae increase in size towards the valve margins ( Fig. 472 ).

Type:— UNITED REPUBLIC OF TANZANIA, Lake Tanganyika , Mahale National Park, at 783 m elevation; sand, 25 m water depth, collected SCUBA diving, 6°10’25.1” S 29°44’25.2” E, W. Salzburger, 28 th June 2019 (holotype designated here, circled specimen BM-108990! = Fig. 466 , isotypes ANSP-GC17219 !, CANA-129339!). Type material CANA-129318. Registration: http://phycobank.org/103702

Pictures of the isolated specimen:— LM micrograph on 1000× magnification ( Fig. S3u ).

Sequence data:— Plastid gene rbc L sequence (GenBank accession: OQ 660291).

Etymology:— The specific epithet ‘ decora ’ refers to the beautiful and ornate pattern of the cribrate areolae.

Ecology and distribution:— This species has been observed in Lake Tanganyika, where the water is predominantly alkaline, moderately mineral-rich and very transparent. Its distribution range is restricted to Mahale National Park in the central sub-basin of the lake, and only very few specimens have been found on the edge of the southern sub-basin at Cape Nangu in Kasaba Bay ( Fig. 1c, e, f ). This extremely rare species inhabits the deep sandy substrates of the lake, where it usually co-occurs with D. kilhamiana sp. nov., D. cocquytiana sp. nov., D. gigantea sp. nov., D. angusta sp. nov., D. serrulata sp. nov., D. major sp. nov., D. salzburgeri sp. nov., and D. latera sp. nov.

Main differential characters:— Valve shape, broad canals, canal areolae arranged in oblong circles, large areolae on the valve, external fin-like ornamentations across the valve, and poroids>25 per areola.

Similar species:— Diploneis serrulata sp. nov. and Diploneis abscondita Lange-Bertalot & Fuhrmann (2016:158) .

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 462–474. Diploneis decora sp. nov., LM (Figs 462–471) and SEM external (Figs 472–474) valve views, Lake Tanganyika.462, 463, 467. Specimens from Cape Nangu at Kasaba Bay. 464–466, 468–474. Specimens from Mahale National Park. Fig. 466. Holotype specimen. 472. View of a whole valve. 473. Half valve, showing canal areolae arranged in oblong circles (white arrow). 474. Distal raphe end with deflected terminal fissure. Scale bars = 10 μm (Figs 462–472), 5 μm (Fig. 473), 3 μm (Fig. 474).

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.