Ulnaria xieriverensis sp. nov., internal view, SEM A a complete valve with valvocopula B, C two complete valves with valvocopula, note undulate valve margins D middle detail from A, note the central area is completely absent and a row of serrated projections over virgae (three arrows) E, F two apical details from A, note serrated projections over virgae (E, three arrows). Scale bars: 10 μm (A–C); 1 μm (D–F).