Ulnaria sangzhi-biseriata sp. nov., internal view, SEM A a valve with a valvocopula B middle part from A, note the serrated projections (two arrowheads) C, D two apical details from A, note the closed nature of valvocopula and serrated projections (arrowheads) E another valve with a valvocopula F apical detail from E, note the serrated projections (two arrowheads). Scale bars: 10 μm (A, E); 2 μm (B–D, F).