Phylogenetic position of the hemiuroid genus <i>Paraccacladium</i> Bray &amp; Gibson, 1977 (Trematoda: Hemiuroidea) and the status of the subfamily Paraccacladiinae Bray &amp; Gibson, 1977

In this study we tested the current taxonomic model of the trematode superfamily Hemiuroidea, according to which the genus <i>Paraccacladium</i> belongs to the family Accacoeliidae. We reconstructed the phylogeny of the hemiuroid Clade A using novel <i>28S rRNA</i> gene sequences of <i>Paraccacladium</i> sp., <i>Derogenes varicus</i>, <i>Progonus muelleri</i> and <i>Lampritrema miescheri</i> as well as data available in GenBank. Based on phylogenetic data, the genus <i>Paraccacladium</i> should be assigned to a separate family, the Paraccacladiidae Bray &amp; 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 <i>Lampritrema</i> is affiliated to the Hirudinellidae. Genetic divergence between North Atlantic and North Pacific isolates of <i>D. varicus</i> was also determined.