Ulnaria constricta-biseriata sp. nov., internal view, SEM A a complete valve with a valvocopula B middle detail from A, note serrated projections at the advalvar edge (two arrows) C, D two apical details from A, note the closed nature of valvocopula and serrated projections at the advalvar edge (two arrows respectively). Scale bars: 20 μm (A); 4 μm (B–D).