Eunotia rudis Cocquyt & M. de Haan, 2016

Cocquyt, Christine, Haan, Myriam De & Ndjombo, Edit Lokele, 2016, Eunotia rudis sp. nov., a new diatom (Bacillariophyta) from the Man and Biosphere Reserve at Yangambi, Democratic Republic of the Congo, Phytotaxa 272 (1), pp. 73-81 : 75-78

Eunotia rudis Cocquyt & M. de Haan , sp. nov. ( Figs 2–24 )

Valve with four undulations on the dorsal side and with straight ventral margin. Ends slightly heteropolar, with one pole more protracted than the other, and both broadly rounded. The slope between the dorsal valve undulation and the pole is steeper near the more protracted pole. Valve face with an irregular rough surface. Length (31.5) 36.0–48.0 μm, width 9.0–13.0 μm. Striae coarse and irregularly distributed on the valve face, 5.5–7.0, rarely up to 8.5 in 10 μm in the middle of the valve, becoming denser towards the poles. Striae radiate almost throughout the valve, except for the ones in the middle of the valve. Short striae often present near the dorsal and the ventral side. Areolae very distinct, usually 24–26 in 10 μm, sporadically up to 28 in 10 μm, and often lacking on parts of the striae. Terminal nodules close to poles. Terminal raphe ends broadly curved on the valve face and clearly visible in LM. Large hyaline area is present around the raphe endings on the mantle side. Striae between the raphe and valve mantle margin denser than on the rest of the valve. Girdle bands with striae, around 25 in 10 μm, composed of large areolae and with clearly visible undulations on the dorsal side. In girdle view, the rough surface of the valve face is visible as a spiny unevenness. Girdle bands with distinct areolae arranged in rows but often irregularly distributed along these rows; around 25 rows in 10 μm.

Type:— DEMOCRATIC REPUBLIC OF THE CONGO. Tshopo Province : Libongo River, 0.804057° N, 24.529932° E, benthic sample CCA 3282 , M. de Haan, 14 November 2013 (holotype BR! 4447, Botanic Garden Meise, Belgium, the valve representing the holotype is here illustrated in Figs 6–7 ; isotype ZU! 10/69 BRM, Hustedt Diatom Collection, Alfred-Wegener-Institut für Polar- und Meeresforschung, Bremerhaven, Germany) .

Etymology:— The specific epithet “ rudis ” refers to the rough look of the outside surface of the valve. SEM observations ( Figs 13–24 ):— Valve face with irregular shallow corrugations ( Figs 13-21 ). Striae composed of slightly elongated areolae oriented in different directions or rarely rounded ( Fig. 21 ). External openings of the areolae obliquely perforating the thick silica wall; externally the areolae are covered by hymenes laying deep in the cell wall ( Fig. 22 arrow). Internally the areolae are rounded ( Fig. 23 ). Terminal nodules relatively close to the ends, expanded between the raphe endings and the poles ( Figs 15–16 , 19–20 ). Terminal raphe fissures short, straight on the mantle and extending onto the valve face with an angle of about 110° ( Figs 15–16 , 19–20 ). Terminal raphe endings enlarged at the valve surface, becoming narrower deeper in the thickened cell wall of the terminal nodule ( Figs 15–16 , 19–20 ). Internally the raphe terminates in a very small helictoglossa near the poles ( Fig. 24 ).A single small rimoportula is present at one of the poles ( Fig. 24 arrow). Spines are absent.

Girdle composed of at least three copulae ( Fig. 17 ). Girdle bands almost smooth with rounded areolae irregular placed on striae ( Figs 18–20 ).

Ecology and distribution:— Species of acid, running freshwater. Known from the Libongo River in the MAB Reserve of Yangambi and the Loile River located between Yangambi and Kisangani, Tshopo Province, D.R. Congo.

Figures

FIGURES 2–12. Eunotia rudis, LM. 2–9.Valve views showing size diminution series. 10–12. Girdle views. 3–4. Same valve taken at different foci. 6–7. Same valve taken at different foci. 10–11. Same frustule taken at different foci. Valves and frustules from the holotype slide BR 4447, Libongo River, Tshopo Province, Democratic Republic of the Congo. 6–7. Valve representing the holotype. Scale bar: 10 μm.

FIGURES 13–18. Eunotia rudis from type material CCA 3282, SEM external views. 13–14. Overview of an entire valve. 15–16. Detail of both poles of the same valve showing the enlarged terminal raphe endings. 17. Overview of an entire frustule in girdle view. 18. Detail of the girdle bands near the undulation on the dorsal side. Scale bar: 10 μm (Figs 13–14, 17), 5 μm (Figs 15–16, 18).

FIGURES 19–24. Eunotia rudis from type material CCA 3282. 19–22. SEM external views. 23–24. SEM internal views. 1–20. Detail of the girdle bands near both poles of the same frustule. 21–22. Details of the areolae, obliquely perforating the thick silica wall; hymen (arrow) laying deep in the cell wall. 23. Overview of an entire valve. 24. Detail of a terminal raphe ending with a small helictoglossa and rimoportula (arrow). Scale bar: 10 μm (Fig. 23), 5 μm (Figs 19–20), 2 μm (21, 24), 1 μm (22).