A–F Achnanthidium anhuense sp. nov., SEM internal views of raphe valve A, B internal view of an entire raphe valve C, D apices of the valve, showing the distal raphe ends E central area of the valve, showing the proximal raphe ends F internal areola openings with fine hymenate structures. Scale bars: 5 µm (A, B); 1 µm (E); 0.5 µm (C, D); 0.3 µm (F).