Ulnaria constricta-biseriata sp. nov., internal view, SEM A a complete valve B middle part from A, note two constricted middle margins and some ghost striae C, D two apical details from A, note the striae mostly biseriate and two helictoglossae E another complete valve F middle detail from E, note two constricted middle margins and some ghost striae. Scale bars: 20 μm (A, E); 2 μm (B–D, F).