Pelagophyceae is a class of heterokont algae. It is the sister group of the Dictyochophyceae. All known species are marine. They can be single-celled (coccoid or flagellate), palmelloid or filamentous. Some members (Pelagomonas) belong to picoplankton, and some other (Sarcinochrysis) are macroscopic attached organisms. The class contains 13 genera, three families and two orders (2017): It is expected that molecular studies will add more species to this list.