The proboscis monkey (Nasalis larvatus) or long-nosed monkey is an arboreal Old World monkey with an unusually large nose, a reddish-brown skin color and a long tail. It is endemic to the southeast Asian island of Borneo and is found mostly in mangrove forests and on the coastal areas of the island. This species co-exists with the Bornean orangutan and monkeys such as the silvery lutung. It belongs in the monotypic genus Nasalis.