Ulnaria shun-biseriata sp. nov., external view, SEM A–C three complete valves, note biseriate striae and variable central areas D, E two apical details from A, note a few serrated projections protruding over the ocellulimbus (three arrows) F details of areolae showing the closing plates. Scale bars: 10 μm (A–C); 1 μm (D–F).