Re‐describing and ascertaining to homeland <scp><i>Hypostomus vaillanti</i></scp> (<scp>S</scp>teindachner, 1877) (<scp>S</scp>iluriformes: <scp>L</scp>oricariidae), a golden and black pleco from <scp>N</scp>ortheast <scp>B</scp>razil

Approximately 26 species of Hypostomus occur in the five freshwater ecoregions in Northeast Brazil. One of these ecoregions is the Parnaíba, which drains almost the entire state of Piauí, and part of the states of Maranhão and Ceará. Among the species of Hypostomus registered in this ecoregion, there is Hypostomus vaillanti. The type locality of H. vaillanti was assigned to the Rio Preto, a tributary of the median portion of the Rio São Francisco basin at the municipality of Villa de Santa Rita (currently Santa Rita de Cássia), Bahia State, Brazil. Despite these historical data, we only found H. vaillanti in the Rio Parnaíba basin. Some fish surveys were carried out in different times by the authors and by other skilled ichthyologists in the Rio Preto and other nearby rivers from the Rio São Francisco basin, and no specimen of H. vaillanti have been found. Additionally, although the original description of H. vaillanti was well written, searching its distinction from some congeners in the taxonomic literature is nowadays quite complicated. Therefore, this species is re-described, and a new diagnosis is provided based on the analysis of recently found specimens in addition to an analysis of the type material. A lectotype of the Plecostomus vaillanti is designated herein. The results suggest that the distribution of H. vaillanti is restricted to the Rio Parnaíba basin; furthermore, we provide a molecular phylogenetic analysis that highlights some relationships between H. vaillanti and closely related species.