Ardissoneopsis appressata sp. nov. A, B flabellate colony and detail showing hemispherical nuclei surrounded by plastids and appressed to girdle faces; arrows on B show two of the many walls between cells (GU68H-1) C middle of colony in oblique view, showing inflation where nuclei are located D base of colony, showing parts of six frustules including pleura (pl, arrow) (GU44AP-2) E–G half valve from Yap, acid cleaned, with details of central and polar portions showing shape and stria density (Y42-1). Scale bars: 100 µm (A); 50 µm (E); 25 µm (B); 10 µm (C, F, G).