On the taxonomic history and true identity of the collared titi, cheracebus torquatus (Hoffmannsegg, 1807) (Platyrrhini, Callicebinae)

The collared titi, Cheracebus torquatus, is paradoxically the least well-defined of the so-called “torquatus group” of Neotropical titi monkeys. Since its description by Hoffmannsegg in 1807, it has been re-characterized numerous times. In this study, the true identity of Cheracebus torquatus is assessed based on a review of its taxonomic history and the observation of 100 skins from across the genus Cheracebus, including the holotype for C. torquatus. We propose that the C. torquatus type specimen and type description fit most closely with widow monkeys found south of the Rio Solimoes between the rios Jurua and Purus, and we conclude that purinus Thomas, 1927, is a junior synonym of torquatus. This necessarily invalidates the torquatus type locality, as defined by Hershkovitz, of Codajas, north (left) bank of the Solimoes, and we thus restrict the type locality to Aiapua, left bank of the Rio Purus, Brazil. The left bank Rio Solimoes populations that were previously classified as C. torquatus (sensu Hershkovitz) are here included as lugens, and we redefine C. lugens to include all Cheracebus found north of the SolimoesJapura-Caqueta. We discuss the broad phenotypic variation found across C. lugens specimens and the existence of three C. lugens lineages in molecular phylogenies, as well as issues with the classification of other forms recognized by Hershkovitz. To conclude, we currently consider the genus Cheracebus to comprise five widow monkey species—torquatus (formerly purinus), regulus, lucifer, medemi and lugens.