AbstractThe genera IsochelesStimpson, 1858 and LoxopagurusForest, 1964 are endemic to America and occur in tropical and subtropical waters. There are five species of Isocheles, two of them are found in the Western Atlantic (I. sawayaiForest & de Saint Laurent, 1968 and I. wurdemanniStimpson 1859) and three in the Eastern Pacific (I. pilosus (Holmes, 1900), I. pacificusBouvier, 1907, and I. aequimanus (Dana, 1852)). Loxopagurus is a monotypic genus and occurs only in southeastern South America. These two genera are morphologically similar, with differences in shape and size of chelae. The published information on the taxonomy of these genera is scant, and there have been some recent doubts about their phylogenetic relationship. Our study aimed to elucidate the phylogenetic relationship of Isocheles and Loxopagurus and evaluate their taxonomic validity and contextualization in Diogenidae Ortmann, 1892. We performed an integrative analysis using multigene data (16S rRNA, COI, and H3) and a detailed morphological evaluation, including redescriptions, seeking characters that allow the clear identification of these species. The type specimens of I. aequimanus, I. pilosus, and L. loxochelis (Moreira, 1901) were lost and errors are common regarding the identification of the species of Isocheles. Characters that clearly delimit these species, such as the ornamentation and shape of the chelipeds and the number of teeth on the second article of the antenna, were stated. The morphological and molecular analyses corroborated the taxonomical validity of Isocheles and Loxopagurus as two distinct genera based on the differences of the shield and chelipeds, on the topology of the trees, and on the genetic divergence inferred from three molecular markers. We also verified that the five amplified species of Isocheles constitute five distinct clades and described a new species of Isocheles, using both molecular and morphological differences from congeners. An identification key for Isocheles is proposed. Although the type material of two out of the five species of Isocheles and the holotype of Loxopagurus loxochelis were lost, the designation of neotypes is not recommended in these cases.