Phylogenetic position of the hemiuroid genus Paraccacladium Bray & Gibson, 1977 (Trematoda: Hemiuroidea) and the status of the subfamily Paraccacladiinae Bray & Gibson, 1977

In this study we tested the current taxonomic model of the trematode superfamily Hemiuroidea, according to which the genus Paraccacladium belongs to the family Accacoeliidae. We reconstructed the phylogeny of the hemiuroid Clade A using novel 28S rRNA gene sequences of Paraccacladium sp., Derogenes varicus, Progonus muelleri and Lampritrema miescheri as well as data available in GenBank. Based on phylogenetic data, the genus Paraccacladium should be assigned to a separate family, the Paraccacladiidae Bray & Gibson, 1977 stat. nov. The morphological differences between the Paraccacladiidae and the Accacoeliidae are the absence of a uroproct, anteriorly directed diverticula of intestinal caeca, and the position of Mehlis’ gland, posterior or postero-lateral to the ovary. Phylogenetic analysis indicates a sister relationship between the Derogenidae and the Sclerodistomidae. It also shows that the Paraccacladiidae, on the one hand, and a group of families, the Accacoeliidae, Hirudinellidae and Syncoeliidae, on the other, share the most recent common ancestor. Our data support the hypothesis that the genus Lampritrema is affiliated to the Hirudinellidae. Genetic divergence between North Atlantic and North Pacific isolates of D. varicus was also determined.