FIGURES 37–40 in Gomphonema frequentiformis (Metzeltin & Krammer) comb. nov. (Bacillariophyta): ecology and taxonomy of a Neotropical diatom

FIGURES 37–40. Common Gomphonema species from the Rio Negro basin (BrazilianAmazon). Figs 37–38. Gomphonema frequentiformis showing external valve overview and detail of the central area with slit-like areolae and apical pore field conspicuous on the footpole. Figs 39–40. Gomphonema archaevibrio showing slight heteropolarity and dorsiventrality. Detail of the central area showing sigmoid slit-like areolae as well. Scale bars = 30 µm (Fig. 39), 10 µm (Fig. 37), 5 µm (Figs 38, 40).