Taxonomic myths and phylogenetic realities in the systematics of the Opisthorchiidae (Trematoda)

Abstract The Opisthorchiidae are a large trematode group with a complex taxonomic structure at the subfamily level. Phylogenetic assessment of the Metorchiinae, the Opisthorchiinae and the Pseudamphistominae was carried out using 28S rDNA, concatenated 18S + 28S rDNA, ITS1 and ITS2 rDNA, and COI mt DNA sequences data set. Phylogenetic analyses showed that Metorchis (Metorchiinae), Pseudamphistomum (Pseudamphistominae), Opisthorchis and Clonorchis (Opisthorchiinae) were grouped in a same clade and that Amphimerus (Opisthorchiinae) has a basal position to all these genera. Thus, the Opisthorchiinae can only be resolved as a monophyletic taxon in combination with metorchiine and pseudamphistomine trematodes. The group comprising opisthorchiines, metorchiines and pseudamphistomines clustered with apophallines and liliatrematines. However, the Apophallinae did not appear as a monophyletic taxon. As a result, two subfamilies of traditional opisthorchiids, the Metorchiinae and the Pseudamphistominae, were not recognized as valid. In addition, we demonstrated the existence of three monophyletic groups of heterophyid trematodes, which is important for the future revision of this group.