Mastogloia senegalensis Van de Vijver, Fofana, Sow & Ector, 2017

Vijver, Bart Van De, Fofana, Cheikh Abdoul Kader, Sow, El Hadji, Cocquyt, Christine, Blanco, Saúl & Ector, Luc, 2017, Morphology of two Mastogloia species (Bacillariophyta) from Lac de Guiers (Senegal) and comparison with the type material of M. braunii, European Journal of Taxonomy 374, pp. 1-23 : 12-16

Mastogloia senegalensis Van de Vijver, Fofana, Sow & Ector sp. nov.

Figs 46–65

Etymology

The new species is named after Senegal, the country from which the new species is described.

Type

SENEGAL: Lac de Guiers, 10 Mar. 2007, B. Van de Vijver sample SEN-42 (holo-: slide no. BR-4500; iso-: PLP-334; University of Antwerp, Belgium).

Description

Light microscopy ( Figs 46–55 )

Valves elliptic-lanceolate with broadly convex margins. Apices slightly protracted, cuneately rounded, never rostrate. Valve dimensions (n = 25): length 26–56 µm, width 11.5–17.0 µm. Axial area narrow, linear-lanceolate, narrowing towards the apices. Lyre-shaped hyaline depression present close to the axial area, separating 1–2 rows of pseudoloculi from the striae. Central area rather small, transapically elliptical to rectangular. Raphe lateral with undulating branches. Proximal raphe endings weakly expanded, coaxial. Distal endings hooked towards the same direction. Striae slightly radiate throughout, becoming more strongly radiate towards the apices, 16–18 in 10 µm. Occasionally one to several shortened striae inserted near the central area ( Figs 46, 48 ). Pseudoloculi well visible in LM, 15–20 in 10 µm. Partecta distributed along the entire partectal ring, closely attached to the margins without broad flange, reaching almost the apices. Partecta of different size (5–7 in 10 µm): the middle 4–5 partecta (length 1.9–3.0 µm, width 1.9–3.1 µm) considerable larger than the outer partecta (length 1.1–1.8 µm, width 1.2–2.0 µm).

Scanning electron microscopy ( Figs 56–65 )

External raphe branches clearly undulating ( Fig. 57 ). Proximal raphe endings simple to very weakly expanded, slightly deflected ( Figs 57–58 ). Distal raphe fissures centrally crossing the terminal nodule, elongated, hooked towards the same direction, continuing onto the valve mantle ( Figs 57, 58 ). No marginal crest on the valve face/mantle junction ( Fig. 59 ). Mantle striae uniseriate near the valve face/ mantle junction, biseriate near the mantle edge, composed of several rounded to irregularly shaped pseudoloculi ( Fig. 59 ). Valve face clearly subdivided into two zones: outer zone composed of uniseriate striae, with up to 3–7 rounded pseudoloculi, central zone restricted to both sides of the raphe-sternum, formed by a shallow, but distinct lanceolate median depression ( Fig. 57 ). Close to the raphe, one row of irregularly scattered rounded pseudoloculi present ( Fig. 58 ), whereas in the depressions on both sides of the axial area, pseudoloculi transapically elongated, rectangular, diminishing in size towards the apices ( Fig. 58 ). Central area slightly raised, thickened. Small hyaline areas present at the apices ( Figs 57–58 ). Shallow irregular depressions sometimes visible in the axial area ( Figs 57–58 ). Internally, hyaline raphe sternum H-shaped lyriform, clearly raised ( Figs 60, 63 ). Well-developed, raised costa-like interstriae interrupted by the raphe-sternum extending from the axial area towards the valve margins, separating the areolae ( Figs 60, 63 ). Inner areolae arranged in groups of 6 per pseudoloculus ( Fig. 62 ). Raphe branches straight with indistinct, slightly deflected proximal endings, terminating on a weakly raised central nodule ( Figs 60, 63 ). Valve apices with small pseudosepta covering the distal raphe endings ( Fig. 65 ).

Girdle composed of the valvocopulae and one open, non-perforated copula ( Fig. 56 ). Valvocopulae with partectal ring, opening near the apices through a series of partectal pores ( Figs 56, 59 ). Partectal ring opening at the poles by a cleft, covering entirely the pseudosepta ( Figs 60–62 ). Lacunae never present ( Figs 61–62 ). Partecta extending almost entirely to the valve apex, with only a small siliceous flange ( Figs 60, 64 ). Partecta subequal in size with the large ones grouped in the middle, the smaller ones nearer to the apices ( Fig. 60 ). Partecta ornamented with several series of small, rounded areolae, loosely aggregated in distinct plaques and arranged inwardly ( Fig. 64 ).

Figures

Figs 46–55. Mastogloia senegalensis Van de Vijver, Fofana, Sow & Ector sp. nov. Light micrographs of valves from the Lac de Guiers type population (Van de Vijver sample SEN-42). 46–51. LM views of several specimens showing variation in valve size and shape (the arrows in Fig. 46 show typical bifurcating striae near the central area). 52–53. LM views of the partectal ring with the partecta. 54. LM view of an entire valve with removed partectal ring showing the pseudosepta. 55. LM view of an entire valve with removed partectal ring showing the valve interior. Scale bar: 10 μm.

Figs 56–59. Mastogloia senegalensis Van de Vijver, Fofana, Sow & Ector sp. nov. Scanning electron micrographs (SEM) of valves from the Lac de Guiers type population (Van de Vijver sample SEN-42). 56. SEM girdle view of an entire frustule showing the partectal pores and the mantle areolae. 57. SEM external view of an entire valve with typical undulating raphe branches. 58. SEM external detail of the apex and the axial area with the depressed grooved on both sides of the raphe. 59. SEM external detail of the valve mantle. Scale bars: 10 µm.

Figs 60–65. Mastogloia senegalensis Van de Vijver, Fofana, Sow & Ector sp. nov. Scanning electron micrographs (SEM) of valves from the Lac de Guiers type population (Van de Vijver sample SEN-42). 60. SEM internal view of an entire valve with the partectal ring. 61–62. SEM internal details of the partectal ring near the valve apices showing the cleft on each apex. 63. SEM internal detail of the central area and part of the partectal ring. 64. SEM internal detail of the partecta showing the partectal walls with 2–4 series of small, rounded pores loosely aggregated in distinct plaques. 65. SEM internal view of a valve apex without the partectal ring (note the small pseudoseptum). Scale bars: 60–63, 65 = 10 µm; 64 = 1 µm.