Ulnaria shun-biseriata sp. nov., SEM, internal view A–C three valves with closed valvocopulae D middle part detail from C note central area flanked by a few marginal striae only on one side and serrated projections over each virga (two arrows) E, F two apical details from C note unornamented valvocopula at both apices (arrow respectively). Scale bars: 10 μm (A–C); 1 μm (D–F).