A new catfish species of the subgenus Trichomycterus (Siluriformes: Trichomycteridae) from south-eastern Brazilian coastal plains

The coastal river basins of southeastern Brazil located within the limits of the Atlantic Forest harbour a diverse fauna of Trichomycterinae catfishes, with new species being continually described in recent years. Here we describe a new species that was previously misidentified in molecular phylogenies as Trichomycterus caipora Lima, Lazzaroto & Costa, 2008, where it was supported as sister to Trichomycterus nigricans Valenciennes, 1832 from the Rio Macacu basin, belonging to a clade that also includes Trichomycterus santaeritae (Eigenmann, 1918) from the Rio Paraíba do Sul basin.

The three species share the presence of nine pectoral-fin rays, a long maxilla that is longer than the premaxilla and a robust opercular patch of odontodes. The new species is diagnosed by a combination of morphological characters involving opercular and jaw dentition, colour pattern, and some morphometric features. It is endemic to the Rio Imbé basin, is the first record of the genus for this basin, and it fills a gap in the knowledge of the geographical distribution of the Trichomycterinae.

Interestingly, the new taxon and its sister species, T. nigricans, have divergent ecomorphological characteristics, with the former one having diurnal habits, and the latter one, nocturnal. Both species are known only from low-altitude areas, a unique condition in the subgenus Trichomycterus.