Mastogloia braunii Grunow

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 : 3-7

Mastogloia braunii Grunow

Figs 1–16

Verhandlungen der Kaiserlich-Königlichen Zoologisch-Botanischen Gesellschaft in Wien 13: 156, pl. 13 fig. 2 ( Grunow 1863).

Type

EGYPT: Sinaï, El-Tor, A. Grunow 23583 – capsule 0645 ( NMW) (raw material).

Description (type material)

Light microscopy ( Figs 1–5 )

Valves elliptic-lanceolate with broadly convex margins and apiculate, cuneately protracted apices. Valve dimensions (n = 5): length 45–80 µm, width 16–21 µm. Axial area narrow, lanceolate, narrowing towards the apices and the central area. Lyre-shaped hyaline (rather deep) depression present parallel to and close to the axial area, separating 1–2 rows of pseudoloculi from the striae. Central area small, transapically rectangular. Raphe lateral with undulating branches. Proximal raphe endings almost not expanded, coaxial. Distal endings hooked. Striae slightly radiate mid-valve, becoming more strongly radiate towards the apices, 15–16 in 10 µm. Occasionally one to several shortened striae inserted within the normal striation pattern near the central area ( Fig. 2 , arrows). Pseudoloculi slightly visible in LM, ca 18 in 10 µm. Partecta distributed along the entire partectal ring, closely attached to the margins without broad flange, reaching almost the apices. Ring composed of partecta of different size (5–6 in 10 µm in the middle, 7–9 in 10 µm near the apices): the middle 6–7 partecta (length 2.4–2.6 µm, width 1.6–3.1 µm) considerable larger than the outer partecta (length 1.2–1.4 µm, width 1.4–1.6 µm).

Scanning electron microscopy ( Figs 6–16 )

External raphe branches clearly undulating ( Fig. 6 ). Proximal raphe endings straight, simple to very weakly expanded ( Figs 6 – 7 ). Distal raphe fissures centrally crossing the terminal nodule, elongated, weakly hooked towards the same direction, continuing onto the valve mantle ( Fig. 6 ). Marginal crest

on the valve face/mantle junction absent ( Fig. 6 ). Mantle striae uniseriate becoming biseriate near the mantle edge, composed of several rounded to irregularly shaped pseudoloculi ( Fig. 9 ). Valve face clearly subdivided into two zones: an outer zone composed of a series of uniseriate striae, composed of a variable number of rounded pseudoloculi and a central zone restricted to both sides of the raphe-sternum, formed by a distinct lanceolate median depression ( Fig. 6 ). Close to the raphe, one row of irregularly scattered rounded pseudoloculi present ( Fig. 7 , arrows), whereas in the depressions on both sides of the axial area, pseudoloculi transapically elongated, rectangular, diminishing in size towards the apices ( Fig. 6 ). Central area flat, hyaline. Small hyaline area present at both apices ( Fig. 6 ). Shallow depressions sometimes visible in the axial area ( Fig. 6 ). Internally, hyaline H-shaped lyriform raphe sternum clearly raised ( Fig. 8 ). Well-developed, raised costa-like interstriae interrupted by the raphe-sternum extending from the axial area towards the valve margins, separating the areolae ( Figs 8, 10 ). Inner areolae arranged in groups of 6–8 per pseudoloculus ( Fig. 10 ). Raphe branches straight with indistinct, almost straight proximal endings, terminating on a weakly raised central nodule ( Fig. 8 ). Valve apices with pseudosepta ( Fig. 11 ). Valvocopulae with typical partectal ring, opening near the apices through a series of partectal pores ( Fig. 12 ). Partectal ring opening at the poles by a cleft, covering entirely the pseudosepta ( Figs 12, 15–16 ). Lacunae clearly present ( Figs 15–16 ). Partecta extending almost entirely to the valve apex, with only a small siliceous flange ( Figs 12–13 ). Partecta subequal in size with the large ones grouped in the middle, the smaller ones nearer to the apices ( Fig. 12 ). Partecta ornamented with several series of small, rounded areolae ( Fig. 14 ).

Figures

Figs 1–5. Mastogloia braunii Grunow. Light micrographs (LM) of valves from the type population (Grunow 23583 – capsule 0645, Vienna, Austria). 1–3. LM views of 3 valves showing variation in valve size and shape. The arrows in Fig. 2 indicate shortened striae near the central area. 3–4. Same valve taken at different foci. 4–5. LM views of the partectal ring with the partecta. Scale bar: 10 μm.

Figs 6–11. Mastogloia braunii Grunow. Scanning electron micrographs (SEM) of valves from the type population (Grunow 23583 – capsule 0645, Vienna, Austria). 6. SEM external view of an entire valve showing the shallow depressions in the axial area, the undulating external raphe branches and the terminal raphe fissures. 7. SEM external detail of the central area. The arrows indicate one row of irregularly scattered rounded pseudoloculi. 8. SEM internal detail of the central area. 9. SEM detail of the valve mantle showing the mantle striae with near the mantle edge, their typical biseriate character. 10. SEM internal view of the striae with the arrangement of the inner areolae. 11. SEM internal detail of the valve apex with the pseudoseptum. Scale bars: 6–9 = 10 µm; 10–11 = 1 µm.

Figs 12–16. Mastogloia braunii Grunow. Scanning electron micrographs (SEM) of valves from the type population (Grunow 23583 – capsule 0645, Vienna, Austria). 12. SEM internal view of an entire valve with the partectal ring and series of partectal pores. 13. SEM internal detail of the partecta with the flange connecting the partecta with the valve margins. 14. SEM internal detail of the partecta showing the partectal walls with 2–4 series of small, rounded pores. 15–16. SEM internal details of the partectal ring near the valve apices showing the cleft with the lacunae. Scale bars: 12 = 1 µm; 13–16 = 10 µm.