Ulnaria pandurata-biseriata sp. nov., external view, SEM A a frustule in valve view B middle part detail from A, showing the central area with a few shortened marginal striae on one side C, D two apical details from A, note some partially triseriate striae (arrows) E another middle part showing the fascia-shaped central area F another apex, note a few serrated projections protruding over ocellulimbus. Scale bars: 10 μm (A); 2 μm (B–F).