Putative relationships among inseminating and externally fertilizing characids, with a description of a new genus and species of Brazilian inseminating fish bearing an anal-fin gland in males (Characiformes: Characidae)

a new inseminating fish species of the family characidae, bryconadenos tanaothoros, from tributaries of the upper rio xingu and upper rio tapajós basins, mato grosso, brazil is described as the type species of a new genus. this new species and the genus are characterized by a glandular organ on the anterior region of the anal fin of sexually mature males, curved lower jaw teeth, and an inseminating reproductive mode. this new genus is hypothesized as most closely related to attonitus, a genus with three inseminating species from peru. bryconadenos and attonitus are suggested as related to certain inseminating, but undescribed characid species of uncertain relationships that are similar in certain respects to species of the glandulocaudine planaltina and to the inseminating species of knodus. these and a few other inseminating characids are included in a previous tentative characid subgroup designated as clade a. no species among a relatively small sample of the many species of the clade a genus bryconamericus were found inseminating, except bryconamericus pectinatus. however, newly collected specimens of b. pectinatus were found to have caudal-fin squamation like that of the species of knodus and this species is here tentatively referred to knodus. our investigations indicate that at least several species of knodus, including the type species, knodus meridae, are not inseminating, but we found two inseminating apparently new characid species that currently would be referred to knodus. these species lack the derived anal-fin rays present in the males of k. pectinatus. other clade a taxa known to be inseminating, such as two species of the large genus creagrutus, three species of monotocheirodon (two undescribed), and the species and genera of the characid subfamily glandulocaudinae are briefly discussed regarding possible relationships to attonitus and bryconadenos. the anatomical aspects of the primary and secondary sexual characteristics of bryconadenos and attonit