Surirella ebalensis 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 : 2-8

publication ID	https://doi.org/ 10.5852/ejt.2015.133
DOI	https://doi.org/10.5281/zenodo.3794695
persistent identifier	https://treatment.plazi.org/id/03FF87A9-CF57-967B-FE32-F8ADFC68DA98
treatment provided by	Carolina
scientific name	Surirella ebalensis Cocquyt & J.C. Taylor
status	sp. nov.

Treatment

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

Figs 1–5 View Fig View Fig View Fig View Fig View Fig

Diagnosis

Valves slightly heteropolar, broadly linear to slightly cuneate with broadly rounded poles and slightly constricted margins in the larger valves, smaller valves not constricted. Apical pole broader than base pole. Length: 39.4–64.5 µm; width: 16.1–19.4 µm, in the constricted part 18.7 µm. Wing projection very distinct, alar canals smaller than fenestrae, 2.2–3.0 in 10 µm. Fenestral bars distinct in LM, 30 in 10 µm. Striae indistinct in LM, 30 in 10 µm. Valve face covered with numerous silica granules and spines. Spines also present on the keel. Porcae perpendicular to the axial axis, reaching the axial area and becoming radiate near the poles.

Etymology

The specific epithet refers to the Lingala word for river which was used in the naming of the expedition, Boyekoli Ebale Congo 2010 (the Study of the Congo River 2010), during which numerous algal samples were collected.

Type material

Holotype

Slide BR 4398 from sample CCA 2070 View Materials , Botanic Garden Meise , Belgium (BR). The valve representing the holotype is here illustrated in Fig. 1A View Fig .

Isotype

Slide Zu10/18 from sample CCA 2070, the Friedrich Hustedt Diatom Collection, Alfred-Wegener- Institut für Polar- und Meeresforschung, Bremerhaven, Germany ( BRM).

Type locality

Oriental Province, DR Congo, Lomami River (0.49339° N and 24.16960° E). Epiphyton on Nymphaea lotus ; collected by François Darchambeau and Ernest Tambwe on 24 Nov. 2012.

Morphological observations using scanning electron microscopy ( Figs 2–5 View Fig View Fig View Fig View Fig )

Axial area narrow to absent near the poles. In the middle of the valve the axial area becomes broader and then larger in the depressions than on the top of the porcae (transapical valve undulations). Porcae perpendicular to the axial axis, becoming radiate near the poles and reaching the axial area but not in the extension of each other near the axial area. Striae biseriate, seldom with uniseriate parts near the axial area ( Figs 2C View Fig , 4B View Fig ), about 30 in 10 µm. Near the fenestrae the striae often become triseriate, sometimes quadriseriate ( Fig. 2D View Fig ), and also present for a short distance on the raphe canal just above the fenestrae. Striae composed of 80–110 areolae in 10 µm. Numerous blunt spines scattered over the valve face ( Fig. 2 View Fig B–F). On the top of the porcae these spines can become large, up to 1 µm ( Fig. 4 View Fig A–B). In the depressions the spines look more like elongated granules. Another kind of ornamentation is also present on the valve face: small granules located on the striae, composed of an areola that seems to secrete silica on the outside of the valve face ( Fig. 4 View Fig C–D). Sometimes all areolae of almost the entire stria have these granules on the valve face. On the inside the elongated granules are characterized by a perforation of the wall ( Fig. 4D View Fig ) that has no rimmed margins as the normal areolae do ( Fig. 5A View Fig ). Blunt spines are also present on the keel; the spines orientated towards the valve face are of different length and arranged on a single transapical row ( Fig. 2B View Fig ). These spines are often transapically elongated near their base, the shorter ones more triangular in shape ( Fig. 4B View Fig ). On the side towards the mantle the spines on the keel are often bifurcated; they are draped over a large part of the indented mantle side, partially covering the fenestrae ( Fig. 3C View Fig ). The mantle face near the edge of the mantle at the junction with the valvocopula is smooth and bears a single row of small areolae and oval silica plaques ( Fig. 3C View Fig ). At the apical pole these silica plaques are replaced by around 10 short spherical shaped silica elements ( Fig. 2F View Fig ). Bi- to triseriate striae are present on the indented mantle face at the level of the fenestrae bars. Fenestrae are broader than the alar canals; 30 fenestral bars in 10 µm. External raphe endings are straight, not enlarged at both poles. Internally the raphe is continuous at the head pole while at the base pole the raphe slit is internally interrupted at different levels. Both slits end in a structure resembling a reduced helictoglossa, lacking the typical lip-like structure, and located farther away from the raphe ending ( Fig. 5 View Fig B–D). The girdle is composed of two bands. The open valvocopula band is not smooth but bears tiny granules ( Fig. 3C View Fig ); the second band with a broad ligula and the same tiny ornamentation except on the part of the ligula that is covered by the valvocopula ( Fig. 3 View Fig A–B).

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 ebalensis sp. nov. was observed in a diatom community dominated by Eunotia bidens Ehrenberg , Frustulia cf. saxonica Rabenhorst, Pinnularia acrosphaeria W. Smith , Luticola muticoides (Hustedt) D.G. Mann , Encyonema minutum (Hilse) D.G. Mann , Stenopterobia anceps (Lewis) Brébisson , Eunotia spp., Cymbopleura sp., Placoneis sp., Caloneis sp. and Neidium sp.