Within the digenean genus Parvatrema (Gymnophallidae) there is a group of species that share a unique feature: parthenogenetic metacercariae in the molluscan second intermediate host (2IH). We found that such species are common at the sea shores in the northern Holartic, and they use several gastropod species as 2IH. Using original primers, we sequenced the cox1 gene fragment for available Parvatrema isolates. As a result we differentiated five species: Cercaria quadriramis, Parvatrema homoeotecnum forma A, Parvatrema margaritense, Cercaria falsicingula, Parvatrema sp. 1. These species differ in their interactions with 2IH: from commensalism in the extrapallial cavity to parasitism in the hepatopancreas and the gonad. A similar path of colonization of molluscan first intermediate hosts could have been passed by protodigenaeans during the formation of their complex life cycles. Phylogeographic reconstruction suggested that the expansion of Parvatrema spp. proceeded from North Pacific to North Atlantic (NA), with two independent transfer events.