ABSTRACT. – A new, monospecific diatom genus, Pierrecomperia gen. nov. (typus generis P. catenuloides), is described. In addition, a new species is described in the genus Cymatosira Grunow, viz. C. minutissima. We also propose two new combinations in the genus Plagiogrammopsis Hasle, von Stosch & Syvertsen, namely P. minima comb. nov. and P. sigmoidea comb. nov. (both formerly placed in Plagiogramma Greville). Plagiogramma parallelum Salah, P. minimum Salah and P. sigmoideum Salah are lectotypified. P. parallelum is synonymized with Brockmanniella brockmannii (Hustedt) Hasle, von Stosch & Syvertsen. Morphological and molecular (18S rDNA and rbcL) evidence firmly places Pierrecomperia in the centric diatom family Cymatosiraceae, which is uniquely characterized by the presence of ocelluli. Like Extubocellulus and Pseudoleyanella, Pierrecomperia is isovalvar and is therefore placed in the subfamily Extubocelluloideae. Like most members of the diatom family Cymatosiraceae, the above-mentioned taxa are confined to coastal shallow water habitats where they have adopted a benthic or tychoplanktonic life-form. Their biogeography and autecology is discussed.