Rhinoxenus bulbovaginatus n. sp. is described from the nose of
Salminus maxillosus (Characidae) collected in the basin of
the Rio Parana, near the city of Porto Rico, State of Parana,
Brazil. The new species can be differentiated from the other
three species in the genus by the morphology of the copulatory
complex, vagina, and ventral anchor. The sister group
relationship of the known species of Rhinoxenus was determined
using techniques of Phylogenetic Systematics (Cladism). The
resulting cladogram (C.I.=100%) indicates that the new species
is most closely related to R. piranhus Kritsky, Boeger and
Thatcher, 1988. The other two species of the genus, R.
arietinus Kritsky, Boeger and Thatcher, 1988 and R. nyttus
Kritsky, Boeger and Thatcher, 1988, both parasites of
Anostomidae fishes, have a paraphyletic position in the
cladogram, suggesting that the origin of at least one of them
can not be associated to cospeciation.