First Record of <i>Cavisoma magnum</i> (Acanthocephala: Echinorhynchida) from Japanese Waters, With Systematic Revision on Cavisomatidae

Cavisoma magnum (Southwell, 1927), the sole member of the genus Cavisoma Van Cleave, 1931 (type genus of Cavisomatidae), is an intestinal parasite of marine fishes in the Indo-Pacific, but molecular data are lacking. We report the first Japanese record of C. magnum, found in the nemipterid fish Pentapodus caninus (Cuvier, 1830) off Okinawa—also the first known host from Nemipteridae. Morphological traits matched previous descriptions, and we obtained new sequences for cytochrome c oxidase I, 18S rRNA, and 28S rRNA genes. Phylogenetic analyses showed that Cavisoma clusters with Rhadinorhynchus Lühe, 1911, while Filisoma Van Cleave, 1928, another genus in Cavisomatidae, is distantly related. These results support the non-monophyly of Cavisomatidae. Based on both molecular and morphological evidence, we propose resurrecting Filisomatidae Van Cleave, 1928 for Filisoma, which differs from Cavisoma and related genera by its filiform cement glands. We also present an amended diagnosis of Cavisomatidae and revise its composition.