Abstract
Detritivores of the fish family Curimatidae are assigned to eight genera, one of which, the Curimatopsis , with only five species, is the least speciose genus and sister to other seven genera in the family. Ongoing morphological investigations reveal, however, the likely existence of additional species. In this study, fifty‐one specimens of Curimatopsis from multiple rivers of the Amazon, Paraguay and Suriname drainages were identified morphologically according to the present species concepts and then barcoded using the universal cytochrome c oxidase subunit I ( COI ) mitochondrial marker. Species delimitation analyses were conducted using Bayesian methods through the general mixed Yule‐coalescent analysis combined with conventional likelihood, genetic distance and haplotypic diversity approaches. We found eleven well‐supported clusters that represent four of the named species and seven cryptic, undescribed species of Curimatopsis . Our results show a clear delimitation of species boundaries constrained by distinct Amazonian river ecotones that may have promoted intrageneric lineage diversification. This is the first of a series of genetic studies applicable to future taxonomic, phylogenetic and evolutionary studies across the Curimatidae.