Micrographs of Ardissonea formosa A whole frustule, length 380 µm, girdle view in SEM, showing isopolarity (Guam: GU44BH-5) B, C light micrographs at two focal planes, apical part of valve showing internal foramina (B arrows), annulus and central costa (C arrowheads) (Jaluit: J5) D SEM of internal aspect showing inner wall with foramina and narrow apical pseudoseptum (arrow) (GU44BJ-2) E internal aspect of valve pole with inner wall missing, showing a central longitudinal costa (arrow) (Yap: Y42-1) F internal view of pole of valve with valvocopula, showing double wall with one central line of foramina, transverse and longitudinal costae showing through the interior wall, and the pores of the valvocopula asymmetrically deflected around the notch (arrow) (Y42-1) G broken frustule showing details of wall structure—inner and outer layers separated by costae, inner layer with foramina—in relation to valvocopula and copula (GU44BJ-4) H pole of frustule showing long fimbriae at tip of copula (arrow) (GU75A-4) I detail of frustule pole in girdle view, showing the three girdle bands with no pores in the external surfaces and the groove in the valvocopula apex (arrow) (GU44BH-5) J details of mid portion of frustule in girdle view, showing a line of pores on the edge of the copula (arrowhead) and on the pleura, and the fimbriate inner edge of the valvocopula (arrow) (GU52R-2). Abbreviations used on figures: VC = valvocopula; cop = copula; pl = pleura. Scale bars: 100 µm (A); 10 µm (B–C, I); 5 µm (D–H, J).