Abstract The genus Protoperidinium is the most diverse of the thecate dinoflagellates in both coastal and offshore environments. This genus consists of c. 300 species ( Hoppenrathetal.2009 ), all of which are completely heterotrophic. Although several different classification schemes in the genus Protoperidinium Berg (formerly the genus Peridinium Ehrenberg) have been proposed by different scientists (e.g. Jörgensen1912 ; Lebour1925 ; Abe´ 1981), the genus has been treated as a well-established taxonomic unit even after the revision of the genus Peridinium by Balech (1974). Since the plate formula and the shape of each plate developed in Protoperidinium species are stable, the combination of plate topology and shape have been regarded as key features for subdivision within the genus and identification of species.