The proboscis monkey (Nasalis larvatus) or long-nosed monkey, known as the bekantan in Indonesia, is a reddish-brown arboreal Old World monkey that is endemic to the southeast Asian island of Borneo.
This species co-exists with the Bornean orangutan. It belongs in the monotypic genus Nasalis, although the pig-tailed langur has traditionally also been included in this genus.
The monkey also goes by the Indonesian name monyet belanda (“Dutch monkey”), or even orang belanda (“Dutchman”), as Indonesians remarked that the Dutch colonisers often had similarly large bellies and noses.
This species of monkey is easily identifiable because of its unusually large nose.
The proboscis monkey is a large species, being one of the largest monkey species native to Asia. Only the Tibetan macaque and a few of the gray langurs can rival its size. Sexual dimorphism is pronounced in the species. Males have a head-body length of 66 to 76.2 cm (26.0 to 30.0 in) and typically weigh 16 to 22.5 kg (35 to 50 lb), with a maximum known weight of 30 kg (66 lb). Females measure 53.3 to 62 cm (21.0 to 24.4 in) in head-and-body length and weigh 7 to 12 kg (15 to 26 lb), with a maximum known mass of 15 kg (33 lb). Further adding to the dimorphism is the large nose or proboscis of the male, which can exceed 10.2 cm (4.0 in) in length, and hangs lower than the mouth. Nevertheless, the nose of the female is still fairly large for a primate. The proboscis monkey has a long coat; the fur on the back is bright orange, reddish brown, yellowish brown or brick-red. The underfur is light-grey, yellowish, or greyish to light-orange. The face is orange-pink. The male has a red penis with a black scrotum. Both sexes have bulging stomachs that give the monkeys what resembles a pot belly. Many of the monkeys’ toes are webbed. source