Herpyllobius piotrowskiae n. sp., a mesoparasitic copepod (Multicrustacea: Copepoda: Cyclopoida), on Iphione fustis Hoagland, 1920 (Annelida, Iphionidae) from Papua New Guinea

The cyclopoid copepod family Herpyllobiidae includes highly transformed mesoparasitic copepods infecting benthic polychaetes. Herpyllobius Steenstrup and Lütken, 1861 is the most diverse genus of the family and currently contains 20 species. The egg-carrying ectosoma of these copepods can be more or less easily detected on the host external surface. Members of Herpyllobius exclusively parasitize polynoid polychaete hosts, including the type species. The study of an iphionid polychaete collected in New Guinea allowed us to find two ovigerous female herpyllobiids belonging to an undescribed species of Herpyllobius (which are here described as a new species, Herpyllobius piotrowskiae n. sp.) that differs from its known congeners in the shape of the endosoma and ectosoma, the structure and number of epigenital processes, and the structure of egg sacs. The known host range of Herpyllobius is thus expanded to the Iphionidae. After Herpyllobius nipponicus Lützen, 1964, the new species is the second member of this cold-temperate genus to be reported from subtropical waters. The placement of H. nipponicus and H. piotrowskiae n. sp. in the currently used species groups within Herpyllobius is discussed, as well as the possible reasons explaining the absence of males and the identity of the iphionid host.