Diploneis serrulata, 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 : 76

Diploneis serrulata sp. nov. (LM Figs 475–505 , SEM Figs 506–517 )

Valves are weakly asymmetric, rhombic to rhombic–elliptical with bluntly round apices ( Figs 475–506 ). The length of the valve is 17–36 μm; and the width is 10–16 μm. The axial area is narrow and slightly expanding into the lanceolate central area ( Figs 477 , 506, 509 ), 1.5–4 μm wide. Externally, the longitudinal canal is lanceolate, slightly expanded in the middle of the valve with four rows of cribrate (<8 poroids) areolae narrowing into one at the valve apices ( Figs 506, 509 ). Internally, a thick non-porous slightly raised silica plate encloses the longitudinal canal ( Figs 512, 513 ). Externally, the raphe is filiform, curved with weakly deflected proximal ends positioned within expanded teardrop depressions ( Figs 506, 509, 510 ). Internally, the raphe is curved with simple proximal and distal ends that are slightly elevated with a small helictoglossa and positioned in a depression formed by the longitudinal canal ( Figs 512–515, 517 ). Striae are uniseriate becoming biseriate towards the valve margins ( Figs 507, 508 ), 11–10(12) in 10 μm. The striae are composed of small round areolae covered with cribra (<10 poroids), 20–25 in 10 μm. The inter-areolar thickenings fin-like ridges serrated with ca. 8–12 notched edges (white arrow in Fig. 511 ). The fin-like ornamentations on the canal are slightly bent into semi-circular shapes (white arrow in Fig. 509 ), positioned towards the striae whereas those of the striae are only slightly bent towards the canal, changing opposite direction only at valve mantle ( Fig. 506 ). Internally, the alveoli open via a single elongated opening covered with a thin silica layer ( Fig. 516 ). A fine serrate edge is present aligning with the mantle margin ( Figs 513, 514, 516 ). The valvocopula is serrated (white arrow in Fig. 507 ).

Type: — REPUBLIC OF ZAMBIA, Lake Tanganyika , Mutondwe Island, at 768 m elevation; sand and shells, 9 m water depth, collected SCUBA diving, 8°43’22.0” S 31°07’24.2” E, A. Indermaur, 9th October 2021 (holotype designated here, circled specimen BM-108979! = Fig. 478 , isotypes ANSP-GC17208 !, CANA-129328!). Type material CANA-129328. Registration: http://phycobank.org/103717

Pictures of the isolated specimen: —LM micrograph on 1000× magnification ( Fig. S3p ).

Sequence data: —Plastid gene rbcL sequence (GenBank accession: OQ 660286).

Etymology: —The specific epithet ‘serrulata’ refers to the small, sawtooth like structures on the fin-like ridge structures that ornament the valve.

Ecology and distribution: — Diploneis serrulata sp. nov. has been observed in Lake Tanganyika in the three sub-basins on the Zambian and Tanzanian sides. In the alkaline, moderately mineral-rich and highly transparent waters, the species occurs in relatively large numbers on muddy and sandy substrates (sometimes with mollusk shells) and on submerged rocks and sand fish craters between 7.5 and 33 m water depth. It has also been found on submerged rocks in the littoral areas at Jakobsen Beach and as free-living tychoplanktonic at 60 m water depth in Mahale National Park, probably due to water currents and turbulence. This small species lives almost everywhere in the lake, including Kalambo Falls Lodge, Isanga Bay, Chituta Bay, Mutondwe Island, Ndole Bay, Mahale National Park, Rukoma area, and Kiganza Bay (see Fig. 1c–f ), together with different species in different locations, but mostly with D. kilhamiana sp. nov., D. salzburgeri sp. nov., D. cristata sp. nov., D. tessellata sp. nov., D. major sp. nov., and D. duplex sp. nov.

Main differential characters: —Valve shape, striae pattern, canals broadly expanded at mid-valve, external thick fin-like ornamentations with up to 14 notches distributed across the valve.

Similar species: — Diploneis decora sp. nov. and Diploneis lusatica Lange-Bertalot & Hofmann (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 475–505. Diploneis serrulata sp. nov., LM valve views, Lake Tanganyika. 475, 479, 480, 485, 488, 490, 491–495, 498, 499, 501. Specimens from Kalambo Falls Lodge. 476–478, 481, 482. Specimens from Mutondwe Island. 483, 484, 486. Specimens from Mahale National Park. 487, 489, 497, 504. Specimens from Kasaba Bay. 496. Specimen from Jakobsen Beach. 500, 502, 503. Specimens from Isanga Bay. 505. Specimen from Chituta Bay. Fig. 478. Holotype specimen. Scale bar = 10 μm.

FIGURES 506–511. Diploneis serrulata sp. nov., SEM external valve views, Lake Tanganyika. 506, 509, 510. Specimen from Isanga Bay. 507, 508, 511. Specimen from Chituta Bay. 506. View of a whole valve. 507. View of the whole frustule, white arrowed serrated valvocopula. 508. Close view of fin-like silica ridges. 509. Central area showing teardrop shaped depressions with proximal raphe ends; white arrowed inter-areolar semi-circular shaped fin ornamentations on the canal. 510. Raphe branch with proximal and distal ends bent to the same side of the valve. 511. Close view of uniseriate becoming biseriate striae; white arrowed the inter-areolar fin-like silica ridges serrated into ca. 8–12 notched edges. Scale bars = 5 μm (Figs 506, 507, 510), 2 μm (Figs 508, 509), 1 μm (Fig. 511).

FIGURES 512–517. Diploneis serrulata sp. nov., SEM internal valve views, Lake Tanganyika. 512, 515–517. Specimen from Mutondwe Island. 513, 514. Specimen from Kiganza Bay. 512, 513. View of a whole valve. 514. Mid-valve, showing alveoli structure and simple proximal raphe ends. 515. Distal raphe endings slightly elevated and distant from the valve apices. 516. Detail opening of the alveoli covered by thin silica layers. 517. Close view of the central area and the proximal raphe ends. Scale bars = 5 μm (Figs 512, 513), 2 μm (Figs 514–517).

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.