Surirella congolensis Cocquyt & J.C. Taylor, 2015

Cocquyt, Christine & Taylor, Jonathan C., 2015, New and interesting Surirella taxa (Surirellaceae, Bacillariophyta) from the Congo Basin (DR Congo), European Journal of Taxonomy 133, pp. 1-15 : 8-12

Surirella congolensis Cocquyt & J.C. Taylor sp. nov.

Figs 6–9

Diagnosis

Valves heteropolar, lanceolate with broadly rounded apical pole and subacute base pole, becoming gradually narrower from the apical pole to the base pole; larger valves slightly constricted mid-valve. Valve length 18.7–33.0, width (4.2) 5.5–6.9 (7.9) µm. Wing projection distinct. Alar canals short, not reaching the axial area, 5.5–6.0 in 10 µm, much smaller than the fenestrae, and rarely becoming denser near the poles. Striae about 30 in 10 µm.

Etymology

The specific epithet refers to the Congo River and the Democratic Republic of the Congo where the samples were collected.

Type material

Holotype

Slide BR 4399 from sample CCA 2071 , Botanic Garden Meise , Belgium (BR). The valve representing the holotype is here illustrated in Fig. 6G .

Isotype

Slide Zu10/19 from sample CCA 2071, the Friedrich Hustedt Diatom Collection, Alfred-Wegener- Institut für Polar- und Meeresforschung, Bremerhaven, Germany ( BRM).

CCA 2071: Lomami River, 0.49339° N and 24.16960° E, epiphyton on dead submerged wood, collected by François Darchambeau and Ernest Tambwe on 24 Nov. 2012.

Type locality

Oriental Province, DR Congo, Lomami River (0.49339° N and 24.16960° E). Epiphyton on dead submerged wood.

Morphological observations on scanning electron microscopy ( Figs 8–9 )

External view

Axial area narrow. Striae biseriate, continuing on the keel also above the fenestrae and on the mantle side. Raphe endings near the apical pole straight not enlarged ( Fig. 8 B–C), near the base pole straight and slightly bent towards the valve face ( Fig. 8D ). Striae composed of round areolae, in 10 µm, biseriate and continuing on the raphe sternum. Fenestrae open and divided by fenestral bars, openings between the fenestral bars located in the prolongation of the striae. No ornamentation such as spines or silica granules present on the valve face, except for silica plaques present at the edge of the valve mantle at the place where the valvocopula is attached to the valve ( Fig. 8E ).

Internal view

Raphe continuous on the apical pole ( Fig. 9A ) and interrupted near the foot pole with straight and slightly expanded raphe endings ( Fig. 9 B–C).

Girdle composed of several open, unornamented bands.

Ecology

Physical and chemical parameters measured at the type locality are as follows: 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, 0.086 mg l-1 soluble reactive phosphorous (SRP).

Surirella congolensis sp. nov. was observed in a diatom community dominated by Navicula feuerbornii var. africana Foged , Gomphonema brasiliense subsp. pacificum Gerd Moser, Lange-Bertalot & Metzeltin , Orthoseira roeseana (Rabenhorst) O’Meara , Eolimna spp. and Eunotia spp.

Figures

Fig. 6. Surirella congolensis sp. nov., from the holotype slide BR 4399, Lomami River, DR Congo, LM (DIC), valve views. G. Valve representing the holotype. Scale bar = 10 µm.

Fig. 7. Surirella congolensis sp. nov., from the holotype slide BR 4399, Lomami River, DR Congo, LM (DIC), girdle views. Scale bar = 10 µm.

Fig. 8. Surirella congolensis sp. nov., type material from sample CCA 2071, Lomami River, DR Congo, SEM. External view. A. Overview. B–C. Detail of foot pole showing the straight not expanded raphe endings (arrow). D. Detail of the apical pole showing the slightly curved raphe endings (arrow). E–F. Detail of the biseriate striae and the open fenestrae with the fenestral bars. Scale bars: A–B = 2 µm; C–F = 1 µm.

Fig. 9. Surirella congolensis sp. nov., type material from sample CCA 2071, Lomami River, DR Congo, SEM. Internal view. A–B. Head pole showing the continuous raphe (arrow). C–D. Foot pole showing the interruption of the raphe and the straight slightly expanded terminal raphe endings. E–F. Detail of the alar canals. Scale bars: B–C = 2 µm; A, D = 1 µm.