Morphological and Molecular Characteristics of Two Species of the Genus Rhadinorhynchus (Palaeacanthocephala: Echinorhynchida) from the Western Pacific

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Rhadinorhynchus Lühe, 1911 consists of acanthocephalans parasitizing migratory fishes. Of about 50 congeners currently assigned in this genus, 10 named and six unidentified species have previously been studied in molecular phylogenetic works; the intrageneric phylogeny and molecular diversity are thus still incompletely understood. In this study, we examined the phylogenetic positions of the two species R. seriolae (Yamaguti, 1963) and R. laterospinosus Amin, Heckmann, and Ha, 2011 based on the cytochrome c oxidase subunit I and 18S rRNA genes determined from material found in the intestines of the Pacific bluefin tuna Thunnus orientalis (Temminck and Schlegel, 1844) (new host) and the frigate tuna Auxis thazard (Lacepède, 1800), respectively. This is the first record of R. laterospinosus from Japan.