Phylogenetic Evidence for the Lissorchiid Concept of the Genus Anarhichotrema Shimazu, 1973 (Trematoda, Digenea)

Abstract

Anarhichotrema Shimazu, 1973 is a monotypic digenean genus, with the type- and only species, Anarhichotrema ochotense Shimazu, 1973, known to infect North Pacific fishes. This genus was originally described as a member of the Lissorchiidae (Monorchioidea) and later moved to the Zoogonidae (Microphalloidea). Its exact phylogenetic position has remained unresolved due to the lack of molecular data. In this study, we isolated specimens of A. ochotense from the Bering wolffish, Anarhichas orientalis Pallas, 1814 caught in the Sea of Okhotsk, described them morphologically and performed a molecular phylogenetic analysis of their nuclear 18S and 28S rDNA regions. The specimens examined in our study generally corresponded to previous morphological descriptions of A. ochotense but were noticeably smaller, possibly due to the crowding effect. The phylogenetic analysis placed Anarhichotrema within the Lissorchiidae as a sister taxon to the group comprising freshwater lissorchiids. Thus, we restore Anarhichotrema to the Lissorchiidae, as originally assigned.