Eight species of Rhinoxenus are reported from nasal cavities of characiform fishes in the Neotropics: Rhinoxenus arietinus Kritsky, Boeger & Thatcher, 1988, from anostomid hosts; R. bulbovaginatus Boeger, Domingues & Pavanelli, 1995, from characid hosts; R. nyttus Kritsky, Boeger & Thatcher, 1988, from anostomid hosts; R. piranhus Kritsky, Boeger & Thatcher, 1988, from serrasalmin hosts; R. anaclaudiae n. sp., from characid hosts; R. euryxenus n. sp., from serrasalmin and anostomid hosts; R. curimbatae n. sp., from prochilodontids hosts; and R. guianensis n. sp., from curimatid hosts. Furthermore, several undeterminate species are reported from Hydrolicus scomberoides (Cynodontidae). Hosts were collected from rivers in Brazil and French Guiana. The hypothesis on the sister-group relationships of species of Rhinoxenus (C.I. = 66%; R.I. = 66%), based on 10 transformation series, is ((R. nyttus, R. curimbatae n. sp.) (R. bulbovaginatus (R. arietinus (R. guianensis n. sp., R. anaclaudiae n. sp. (R. euryxenus n. sp., R. piranhus))))). Coevolutionary analysis suggests that events of cospeciation, duplication, dispersion, and extinction are required to explain the observed host-parasite association. The origin of R. curimbatae n. sp., R. nyttus, R. bulbovaginatus, R. anaclaudiae n. sp., and the ancestor of R. piranhus + R. euryxenus n. sp. are putatively associated with events of cospeciation with the ancestors of their respective host families. Dispersion with subsequent allopatric speciation to Anostomidae and Curimatidae appear associated with the origins of R. arietinus and R. guianensis n. sp., respectively. Extinction is necessary to explain the absence of Rhinoxenus spp. on several other characiform families, although sampling density cannot be discarded.
Platyhelminthes, Monogenoidea, Dactylogyridae, Ancyrocephalinae, Characiformes, phylogeny, coevolution, new species.