Phylogenetic Position of Trichomycterus payaya and Examination of Osteological Characters Diagnosing the Neotropical Catfish Genus Ituglanis (Siluriformes: Trichomycteridae).

The Trichomycterinae is among the most diverse catfish groups in the world, with interesting ecological specializations; however, the taxonomy of Trichomycterinae is still problematic, mainly due to unclear limits and diagnoses of the eight included genera. Herein we infer the phylogenetic position and generic placement of Trichomycterus payaya, a recently described species from north-eastern Brazil, with unique morphological features among congeners. A multigene analysis including fragments of two nuclear and two mitochondrial genes (total of 2974 bp) for 53 trichomycterine taxa and three outgroups clearly supports inclusion of T. payaya in Ituglanis, a trichomycterine genus containing 29 valid species, which is corroborated by osteological characters. An examination of osteological characters used to diagnose Ituglanis in its original description indicates that a rudimentary or absent posterior cranial fontanel is synapomorphic for Ituglanis, but this is reversed in I. payaya; an anteriorly directed antero-lateral extremity of the sphenotic-prootic-pterosphenoid complex and a narrow and long lateral process of the parurohyal are synapomorphic for Ituglanis, but homoplastically occurring in other trichomycterids; and the presence of a deep medial concavity on the autopalatine is ambiguous to diagnose Ituglanis by occurring in other closely related trichomycterine taxa. Ituglanis is also distinguishable from other trichomycterines by a unique shape of the metapterygoid and by a reduced number of ribs. The analysis supports a clade, comprising I. payaya and I. paraguassuensis, that is endemic to the Chapada Diamantina, in the semiarid Caatinga of north-eastern Brazil, reinforcing the importance of this region for trichomycterid diversification. By integrating molecular analysis and comparative morphology, the present study provides a more solid basis for delimiting Ituglanis, creating a better taxonomical resolution of the Trichomycterinae, although much more research is necessary to reach a consistent generic classification for the entire subfamily.