Nasalis larvatus (von Wurmb, 1781), proboscis monkey, is the only member of its genus and is the largest colobine monkey. It has a uniquely large nose in males. It occurs in lowland riverine forests, peat swamps, and mangrove swamps of Borneo. It is a strong swimmer and can swim underwater. A folivore, it lives in single male-multifemale troops or all-male groups, in a multilevel social system. Male dispersal is routine and females commonly transfer among groups. It is listed as “Endangered” by the International Union for Conservation of Nature and Natural Resources and is included in Appendix 1 of the Convention on International Trade in Endangered Species of Wild Fauna and Flora.