Mastogloia belaensis M.Voigt

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 : 7-12

Mastogloia belaensis M.Voigt

Figs 17–45

Journal of the Royal Microscopical Society ser. 3 75: 189, pl. 1 fig. 1, 5, 6, 7 ( Voigt 1956).

Description ( Senegal population)

Light microscopy ( Figs 17–32 )

Valves lanceolate to elliptic-lanceolate with convex margins. Apices non-protracted, acutely rounded to slight protracted, subrostrate. Valve dimensions (n = 50): length 31–99 µm, width 11.5–20.0 µm. Axial area narrow, lanceolate, narrowing towards the apices. Lyre-shaped hyaline zone present close to the axial area, separating one row of pseudoloculi from the striae. Central area rather small, rectangular. Raphe lateral with clearly undulating branches. Proximal raphe endings indistinct, straight. Distal endings hooked towards the same direction. Striae radiate throughout, becoming less radiate and even parallel to slightly divergent ( Fig. 25 ) towards the apices, 13–15 in 10 µm. Pseudoloculi quite large, well visible in LM, 15–20 in 10 µm. Partectal ring clearly displaced towards the middle of the valve, composed of partecta of different size (6–8 in 10 µm): the middle 4–8 partecta (length 1.9–2.9 µm, width 1.8–3.9 µm) considerable larger than the outer partecta (length 0.9–1.4 µm, width 1.2–1.8 µm).

Scanning electron microscopy ( Figs 33–45 )

External raphe branches clearly undulating ( Fig. 34 ). Proximal raphe endings simple, very weakly expanding, slightly deflected ( Figs 34–35 ). Distal raphe fissures centrally crossing the terminal nodule, elongated, hooked towards the same direction, continuing onto the valve mantle, terminating almost near the mantle edge ( Fig. 36 ). Very low, slightly thickened marginal crest visible on the valve face/ mantle junction separating the striae on the valve face from the mantle areolae by a hyaline line ( Fig. 34 ). Mantle striae entirely uniseriate, composed of several, usually transapically elongated to slit-like pseudoloculi ( Figs 33–34, 36, 38 ). First pseudoloculi near the junction rounded ( Figs 36, 38 ). Valve face almost flat, subdivided into two zones: outer zone composed of uniseriate striae, with up to four rounded pseudoloculi, central zone formed by one row of rounded pseudoloculi close to the axial area and one row of transapically elongated rectangular pseudoloculi ( Figs 34–35 ). Near the central area, rectangular pseudoloculi replaced by 1–2 small, rounded ones whereas near the apices, central transapically elongated pseudoloculi absent, outer zone with rounded pseudoloculi reaching the axial area ( Fig. 36 ). Shallow depressions sometimes visible in the axial area ( Figs 34–36 ). Hyaline areas present on each valve apex ( Fig. 36 ). Internally, raphe sternum lyriform, slightly raised ( Figs 39, 42 ). Raised thickened costa-like interstriae interrupted by the raphe-sternum extending from the axial area towards the valve margins, separating the areolae ( Figs 42–43 ). Inner areolae arranged in groups of 4–8 per pseudoloculus ( Fig. 45 ). Raphe branches straight with indistinct, coaxial proximal endings, terminating on a raised central nodule ( Figs 39, 42 ). Valve apices with clear pseudosepta covering the distal raphe endings ( Fig. 43 ).

Girdle composed of the valvocopulae and one open, non-perforated copula ( Figs 33, 37 ). Small siliceous papillae present on the copula ( Fig. 37 ). Valvocopulae with typical partectal ring, opening near the apices through a series of elongated partectal pores ( Figs 33, 37–38 ). Partectal ring open, one end closed but with a cleft forming a narrow lacuna ( Fig. 40 ), other split with a cleft ( Fig. 41 ), covering entirely the pseudosepta. Partecta extending to almost ¼ to 1/6 from the valve apex, clearly separated from the valve margin by a siliceous flange ( Fig. 39 ). Partecta subequal in size with the large ones grouped in the middle, the smaller ones closer to the apices ( Fig. 39 ). Partecta ornamented with several series of small, rounded areolae, loosely aggregated in very unclear plaques and arranged inwardly ( Fig. 44 ).

Figures

Figs 17–23. Mastogloia belaensis M.Voigt. Light micrographs (LM) of valves from the Lac de Guiers population (Van de Vijver sample SEN-42). LM views of several specimens showing variation in valve size and shape. Scale bar: 10 μm.

Figs 24–32. Mastogloia belaensis M.Voigt. Light micrographs (LM) of valves from the Lac de Guiers population (Van de Vijver sample SEN-42). 24–28. LM views of several smaller valves showing variation in valve size and shape. 29–30. LM views of the partectal ring with the partecta. 31. LM view of an entire valve with removed partectal ring showing the pseudosepta (arrows). 32. Entire frustule in girdle view. Scale bar: 10 μm.

Figs 33–38. Mastogloia belaensis M.Voigt. Scanning electron micrographs (SEM) of valves from the Lac de Guiers population (Van de Vijver sample SEN-42). 33. SEM girdle view of an entire frustule showing the partectal pores and the mantle areolae. 34. SEM external view of an entire valve with typical undulating raphe branches. 35. SEM external detail of the central area. 36. SEM external detail of the valve apex. 37. SEM external detail of the apices and girdle bands of an entire frustule. 38. SEM external detail of the valve mantle with the transapically elongated mantle areolae and the row of rounded pseudoloculi on the valve face/mantle junction. Scale bars: 10 µm.

Figs 39–45. Mastogloia belaensis M.Voigt. Scanning electron micrographs (SEM) of valves from the Lac de Guiers population (Van de Vijver sample SEN-42). 39. SEM internal view of an entire valve with the typical partectal ring. 40–41. SEM internal details of the partectal ring near the valve apices showing the cleft with the lacunae. 42. SEM internal detail of the central area. 43. SEM internal detail of the valve apex with the pseudoseptum. 44. SEM internal detail of the partecta showing the partectal walls with 2–4 series of small, rounded pores. 45. SEM internal view of the inner areolae arranged in groups of 4–8 per pseudoloculus. Scale bars: 39–43 = 10 µm; 44 = 5 µm; 45 = 1 µm.