Gomphonema grande B. Karthick, Kociolek, J.C. Taylor & Cocquyt, 2016

Karthick, Balasubramanian, Kociolek, J. Patrick, Taylor, Jonathan C. & Cocquyt, Christine, 2016, Gomphonema grande sp. nov., a new diatom (Bacillariophyta) from the Democratic Republic of the Congo, Tropical Africa, Phytotaxa 245 (3), pp. 187-196 : 188-189

Gomphonema grande B. Karthick, Kociolek, J.C. Taylor & Cocquyt , sp. nov. ( Figs 1–24 )

Valves lanceolate-clavate, head pole broadly apiculate, foot pole rounded. Length 46–72 μm, breadth 10–12 μm. Axial area straight, usually with a mottled appearance, expanded to form an asymmetrical, elliptical central area. A prominent stigma present in the central area. Raphe broadly lateral, straight. External proximal raphe ends dilated, distinct. External distal raphe ends deflected towards the direction opposite the stigma opening. Striae radiate around the central area, becoming parallel towards the poles, convergent at the head pole, strongly radiate at the foot pole. Striae broad, comprised of two rows of areolae. Striae number 10–12/10 μm. Bilobed apical pore field prominent at the footpole. Septa and pseudosepta present at both poles.

Type:— DEMOCRATIC REPUBLIC OF THE CONGO. Oriental Province: Lomami River, 0.49339° N, 24.16960° E, epiphytic sample on dead submerged wood sample CCA 2071 (holotype BR 4426, valve representing the holotype here illustrated as Fig. 2 , isotype PUC 13-572)

Etymology:— The specific epithet ‘ grande’ refers to the generally large size of the cell and distinct nature of the ornamentation.

Description:— In the SEM, the valve exterior appears rugose with a network of silica present along the striae, a raised area of silica is present along the margin ( Figs 11–17 ). A single, small spine is present at the head pole at the junction of the valve face and the valve mantle tapering off in a shallow silica ridge on the valve mantle ( Figs 11–17 ). Areolae appear to be sunken within elevated outlines of silica ( Figs 11, 12, 15 ). The axial area has many depressions along its entire length ( Figs 11, 13 ). Distal raphe ends are deflected far onto the valve mantle ( Figs 11, 12, 14 ). Proximal raphe ends are tear-drop shaped, and the stigma opening is elliptical in outline ( Figs 11, 13 ). Areolar openings are occluded by siliceous flaps that form C-shaped openings ( Figs 13, 15, 16 ). Apical pore fields are bisected by deflected distal raphe ends ( Fig. 14 ). Porelli are small, and physically differentiated from the areolae ( Figs 11, 14, 17 ) and extend from the valve face onto the mantle. Areolae extend on to the mantle, and also occur in depressions surrounded by raised silica ( Figs 15–17 ). The valve interior is dominated by a prominent central nodule, helictoglossae and pseudosepta ( Figs 18–24 ). At the poles, pseudosepta are evident, but not extensive ( Fig. 18 ). Helictoglossae are positioned near the valve terminus, and offset from the main raphe branches ( Figs 18, 19, 21, 24 ). The virgae appear slightly undulate (arrow in Figs 20, 21 ), with small silica extensions present ( Figs 18–23 ). The central nodule is raised internally, and the internal proximal raphe ends are recurved against the edges of the nodule. The internal stigma opening appears similar to the helictoglossae, bordered by thickened extensions and giving a lip-like appearance ( Figs 18, 20, 23 ). At the foot pole, porelli are distinct, the lobes of the apical pore fields are separated by the extension of the axial area ( Figs 21, 24 ). Striae extend from the valve face to the mantle ( Fig. 22 ). Girdle composed of several open, smooth bands. At least one band with a row of small poroids near the edge away from the valve ( Fig. 15 ).

Ecology:— Freshwater, epiphytic, acidophilic taxon. At the sampling site in the Lomami River the following characteristics were measured on 24 November 2012 at the time of sampling: water temperature 25.7 °C, pH 6.06, conductivity 22.2 μS cm-1, 0.060 mg l-1 NH 4, 0.005 mg l-1 NO 2, 0.446 mg l-1 NO 3, and 0.086 mg l-1 SRP.

Distribution:— only known from the type locality.

Figures

FIGURES 1–10. Gomphonema grande, LM (DIC). Valve views showing size diminution series. Valves from the type slide BR 4426, Lomami River, Oriental Province, Democratic Republic of the Congo. 2. Valve representing the holotype. Scale bar: 10 μm.

FIGURES 11–17. Gomphonema grande from type material CCA 2071, SEM external views. 11. Whole valve exterior showing raised area of silica along the margin and sunken areolae within elevated outlines of silica. 12. Head pole showing single, small spine tapering in a shallow silica ridge on the valve mantle, and distal raphe curves onto valve mantle. 13. Central area showing tear drop shaped proximal raphe ends, stigmal opening and depressions. 14. Foot pole, with apical pore field composed of round porelli, physically and morphologically distinct from the areolae. 15. Girdle view of head pole with one spine on each valve. 16. View of valve showing the “C” shaped areolae extend on to the mantle. 17. Girdle view of the foot pole showing porelli extend on to the mantel and girdle band. Scale bar: 10 μm (Fig. 11), 4 μm (Figs 12–17).

FIGURES 18–24. Gomphonema grande from type material CCA 2071, SEM internal views. 18. Whole valve internal view showing prominent central nodule, pseudosepta and helictoglossae. 19. Head pole showing helictoglossa offset from the main raphe branches and pseudoseptum. 20. Raised central nodule showing raphe ends recurved against the edge of the nodule and “lip-like” internal stigma opening. 21. Foot pole showing porelli, lobes of the apical pore field and helictoglossa. 22. Internal valve showing the extension of striae to the mantle. 23. Tilted view of raised central nodule with lip-like internal stigma opening. 24. Foot pool showing the helictoglossa and pseudoseptum. Scale bar: 10 μm (Fig. 18), 3 μm (Figs 12–17).