FIGURES 19–29. Gomphonema frequentiformis comb. nov. SEM. Fig. 19. External valve outline overview. Sinuous raphe and heteropolar valves. Fig. 20. Internal valve. Fig. 21 in Gomphonema frequentiformis (Metzeltin & Krammer) comb. nov. (Bacillariophyta): ecology and taxonomy of a Neotropical diatom

FIGURES 19–29. Gomphonema frequentiformis comb. nov. SEM. Fig. 19. External valve outline overview. Sinuous raphe and heteropolar valves. Fig. 20. Internal valve. Fig. 21. Detail of central area showing rounded isolated pore ('stigma') and sigmoid slit-like areolae. Striae not interrupted in the valve face-mantle junction. Proximal raphe endings rounded. Figs 22–23. Internal detail of central area showing transversely elongated isolated pore located in a long groove. Strongly hook-shaped proximal raphe ending. Areolar openings are large and round without internal occlusions, located in а deep foraminal row between strongly silicified vimines. Figs 24–27. Detail of apical (24, 25) and footpoles (26, 27) showing the presence of apical pore field on both apices. Raphe slightly curved to the same side. Figs 28–29. Internal detail of both apices showing the helictoglossae and the slit-like internal areolae openings. Note the pseudoseptum present at both apices (a silica plate extending internally from the apical portion of the valve). Scale bars = 10 µm (Figs 19, 20), 4 µm (Fig. 21), 3 µm (Figs 24–27), 2 µm (Figs 22, 23, 28, 29).