Integrative taxonomy reveals four new species of the armoured catfish genus Pareiorhina (Siluriformes: Loricariidae) from the upper Paraná River basin, Brazil.

Four new species of the small-sized armoured catfish genus Pareiorhina are described from mountain ranges in the Grande River drainage, upper Paraná River basin, based on morphological and molecular species delimitation methods. Molecular analyses based on the cytochrome oxidase subunit I (COI) marker recovered Pareiorhina as polyphyletic, with none of the 11 nominal species, including the 4 newly described, forming a clade with the type species Pareiorhina rudolphi. Instead, two sister clades were recovered outside P. rudolphi: one comprising species with a postdorsal ridge and unicuspid teeth, and another lacking the ridge and bearing bicuspid teeth. The four new species resemble Pareiorhina carrancas and Pareiorhina hyptiorhachis, both readily distinguished by the presence of a postdorsal ridge and simple teeth, and differ from all congeners by unique combinations of body colouration, abdominal plating, vertebral counts, pelvic girdle morphology and morphometric traits. These results underscore the underestimated diversity of the upper Paraná River basin and reinforce the need for continued ichthyofaunal surveys. Furthermore, they highlight the importance of integrating morphological and molecular data to unravel species diversity and distribution patterns of small-sized fish species inhabiting southeastern Brazilian headwaters.