rimoportula

— Many araphid diatoms have parallel striae and a distinct sternum; many araphid diatoms (and even some centric diatoms, particularly in the Biddulphiaceae and Eupodiscaceae) have apical pore fields; other small araphid pennates (such as Staurosira species) and centrics (Corethron and Leptocylindrus) lack rimoportula; and occluded pores are found in most diatoms, albeit in a variety of siliceous structures.