Valve and girdle band morphogenesis in a bipolar centric diatom Plagiogrammopsis vanheurckii (Cymatosiraceae, Bacillariophyta)

Figures & data

Figs 1–4. Plagiogrammopsis vanheurckii mature cells. Strain s0435, light microscopy (Figs 1, 2) and strain s0432, scanning electron microscopy (Figs 3, 4). Fig. 1. Chain of living cells. Fig. 2. Cleaned process valve. Fig. 3. External view of pilus valve. Arrow indicates wing on pilus. Fig. 4. Internal view of process valve. Scale bars: 10 µm.

Figs 5–8. Plagiogrammopsis vanheurckii, strain s0433 (Figs 5, 8) and strain s0435 (Figs 6, 7). Early stages of valve morphogenesis, scanning electron microscopy. Fig. 5. Valve with a distinct annulus, in which silica deposition has not commenced. Fig. 6. Pair of sibling valves showing different stages of development. Arrow indicates annulus of younger valve. Fig. 7. Enlarged view of the annulus shown in Fig. 6. Fig. 8. Valve with distinct annulus, in which silica deposition is nearly complete. Scale bars: 5 µm (Figs 5, 6) and 2 µm (Figs 7, 8).

Figs 9–14. Plagiogrammopsis vanheurckii, strain s0432. Middle stages of valve morphogenesis, external view, scanning electron microscopy. Fig. 9. Silica deposition nearly completed inside annulus. Fig. 10. Plain disc at centre. Note presence of pseudoseptum beneath the disk. Arrow indicates row of base of marginal spines. Fig. 11. Fascia at centre. Arrow indicates base of marginal spines. Arrowhead indicates small areola where rimoportula will be formed. Fig. 12. Apex formation. Note distinct row of marginal spines. Fig. 13. Valve margin thickening. Fig. 14. Fully developed valve face and mantle, but apices not yet formed. Scale bars: 5 µm.

Figs 15–17. Plagiogrammopsis vanheurckii, strain s0434 (Figs 15, 17) and strain s0432 (Fig. 16). Final stages of valve morphogenesis, external view, scanning electron microscopy. Fig. 15. Valve apex formation, ocelluli still unformed (strain s0434). Fig. 16. Almost mature valve during cribrum formation (strain s0432). Fig. 17. Mature valve (strain s0434). Scale bars: 5 µm.

Figs 18–21. Plagiogrammopsis vanheurckii, strain s0433 (Fig. 18) and strain s0432 (Figs 19–21). Middle stages of valve morphogenesis, internal view, scanning electron microscopy. Fig. 18. Valve during radial expansion with pseudoseptum on the central disc. Fig. 19. Marginal thickening started around fascia. Note the valve margin is incomplete. Fig. 20. Lanceolate valve outline complete. Fig. 21. Three-dimensional valve framework complete. Note rimoportula on right hand side of pseudoseptum. Scale bars: 5 µm.

Figs 22–29. Plagiogrammopsis vanheurckii, strain s0432. Formation of areolae (Figs 22–25) and cribra (Figs 26–29), scanning electron microscopy. Valve centre lies on the left side in Figs 22–25. Fig. 22. Centrifugal extension of two semi-circular arms. Fig. 23. Tips of arms fuse at opposite side to form areola. Fig. 24. Thickening starts at fused site. Fig. 25. Thickening proceeds centripetally. Fig. 26. Bases of cribra seen as knobs. Figs 27, 28. Centripetal cribrum formation. Fig. 29. Mature cribra. Scale bars: 0.1 (Figs 22–25) and 0.5 µm (Figs 26–29).

Figs 30–34. Plagiogrammopsis vanheurckii, strain s0432. Band formation, scanning electron microscopy. Fig. 30. Early stages of band formation comprise longitudinal (arrow) and transverse (arrowhead) ribs. Fig. 31. Middle stage. Figs 32, 33. Final stage. Fig. 34. Mature band. Scale bars: 0.5 µm.

Fig. 35. Diagram of formation order of valve elements during valve morphogenesis in Plagiogrammopsis vanheurckii. ¹Annulus becomes disc when silica deposition inside annulus is completed.