Morphological and molecular data reveal a species complex within <i>Gracilinanus aceramarcae</i> (Tate, 1931)

Abstract Gracilinanus aceramarcae is a small opossum distributed in the montane forests from northern Peru to northern Bolivia. This species has been proposed as a species complex; but no study has included specimens from its full distributional range to assess its taxonomic status. Here, we present a review of specimens identified as G. aceramarcae (including new records) based on morphological, morphometric, and phylogenetic analyses using cytochrome b sequences. Our results suggest that G. aceramarcae comprises a Bolivian morphotype (which include the holotype) and seven Peruvian morphotypes distributed allopatrically throughout the Peruvian montane forests. These morphotypes are distinguished by a combination of external and craniodental traits and different position in the morphospace. Five of them were recovered monophyletic in our molecular analyses and were genetically distinct from each other in a range of 6.03–14.13 %. The other two morphotypes were not phylogenetically resolved due to lack of tissues. In conclusion, G. aceramarcae sensu stricto is redescribed, and evidence is provided that the Peruvian morphotypes might constitute putative new taxa. Additionally, we suggest that important rivers such as Marañón, Huallaga, Apurímac, and Limbani have influenced the diversification of these taxa.