Ulnaria sangzhi-biseriata sp. nov., girdle view, SEM A a partly collapsed frustule B middle part from A, note variable central mantles and serrated projections of valvocopula (three arrowheads) C, D two apical details from A, showing four girdle bands associating the epivalve (labelled B1–B4). Scale bars: 10 μm (A); 2 μm (B–D).