FIGURES 20–31 in Taxonomy, distribution and autecology of Planothidium bagualensis sp. nov. (Bacillariophyta) a common monoraphid species from southern Brazilian rivers

FIGURES 20–31: Planothidium bagualensis SEM views. Fig. 20. External view of rapheless valve. Fig. 21. Internal view of rapheless valve with prominent cavum. Fig. 22. External view of raphe valve. Fig. 23. Internal view of raphe valve. Fig. 24. External detail of central area showing expanded and ligulated proximal raphe endings. Reduced striae forming a rounded wide central area. Striae composed (usually) 3–4 rows of small areolae. Fig. 25. Internal detail of raphe valve showing proximal raphe ends. Fig. 26. External detail of valve extremity of rapheless valve. Striae usually triseriate, interrupted at valve mantle junction. Groups of 4–6 areolae present on mantle at end of each striae. Figs 27–28. Detail of cavum aperture. Note the extremities of the border attached to neighbour striae. Figs 29–30. Terminal raphe ending. Note the higher number of areoale in the raphe valve with striae composed of rows with 4–5 round poroids, irregularly placed toward the ends. Areolae very scarce in valve mantle. Fig. 31. Internal view of rapheless valve areaolae. Scale bars: Figs 20–23, 26 = 5 µm; Figs 24–25, 28–30 = 3 µm; Figs 27 = 2 µm; Fig. 31 = 1 µm.