Normal valve of Ulnaria ulnabiseriata, external view, SEM A complete valve B middle detail, note the rectangular central area C, D two apices, note centrally located sternum and rostrate apices E, F apical details, note inset ocellulimbus and some outgrowths protruding over it (F, three arrows). Scale bars: 20 μm (A); 3 μm (B, C, E); 1 μm (D, F).