Abstract
Within Leptoceridae, the genus Oecetis contains about 500 species around the world, including 53 in the Neotropics. In Brazil, there are 15 recorded species of Oecetis. These species were described over several decades by numerous authors with the results that descriptions are not comparable and diagnoses are incomplete. Also, the apparently unbranched M vein, in the forewing, a diagnostic character for Oecetis pointed by McLachlan, is controversial and no consensus has been reached about its homology. Additionally, the only revision for the genus was never published; thus the information and proposed taxa are not available according to the International Code of Zoological Nomenclature. We analyzed specimens collected in the Brazilian Northeast Region and compared these with described species and literature descriptions and Oecetis from other regions. We provide herein the description of five new species, additional characters for diagnosing seven of the species recorded from Brazil, new distributional records, and a dichotomous key to the Brazilian species. Additionally, we contrast the two hypotheses of forewing M vein homology and support the unbranched hypothesis. In this way, we improve the knowledge of the genus in the Neotropics, making the species descriptions comparable in a way that facilitates species identification.