FIGURES 40–54 in Bicudoa amazonica gen. nov. et sp. nov. (Bacillariophyta)-a new freshwater diatom from the Amazon basin with a complete raphe loss in the Eunotioid lineage

FIGURES 40–54. SEM of several eunotioid elements: Figs 40–41 Perforated and opened valvocopula and detail of short internal raphe slit of Eunotia ventriosa var. brevis. Rimoportulae not visible; note the alternating short striae at the dorsal valve mantle and the thick apical cell wall; Fig. 42 Detail of internally uncovered areolae of E. ventriosa var. brevis; Figs 43–45 Bicudoa amazonica: Fig. 43 Detail of external uncovered areolae; Fig. 44 Transversal view of the valve face showing areolae aperture not covered and thick silicified cell wall; Fig. 45 Apex detail of B. amazonica with no external raphe nor apical pore field; Fig. 46 Detail of E. ventriosa var. brevis in oblique external view showing well developed raphe branch and perforated connective bands; Figs 47–54 SEM of different Eunotia species from the Brazilian Amazon showing distinct external and internal evolutionary patterns of raphe system: Fig. 47 Eunotia siolii Hustedt—Holotype (AM 1310). Raphe located mainly on the ventral valve mantle; Fig. 48 Eunotia synedraeformis Hustedt. Prominent "J" shaped raphe with dilated distal and proximal ends; rimoportulae aperture distinct; Fig. 49 Eunotia tapacumopsis Metzeltin & Lange-Bertalot. Large raphe slit located on the valve mantle and valve face; Fig. 50 Eunotia sp. from the Rio Negro with prominent spines and areolae covered externally by velum; Figs 51–52 Eunotia waimiriorum C.E. Wetzel. Reduced raphe system (white arrows) and poorly developed helictoglossae; Fig. 53 Eunotia bidens Ehrenberg. Note internal arrangement of the striae areolae aligned in a narrow "ditch" as in Fragilariforma hamiltonii; Fig. 54 Eunotia sp. showing a well developed helictoglossa. Scale bars: Figs 40–41, 45–47 and 53–54: 5 µm; Figs 42–44: 0.5 µm; Fig. 48: 2 µm; Fig. 49: 3 µm; Figs 50–52: 1 µm..