Species ( Nasalis larvatus , family Cercopithecidae) of long-tailed arboreal Old World monkey of swampy mangrove forests on Borneo.
Diurnal vegetarians, they live in groups of about 20. They are red-brown with pale underparts; the young monkey has a blue face. The male's nose is long and pendulous, the female's is smaller, and the young's is upturned. Males are 22–28 in. (56–72 cm) long, have a 26–29-in. (66–75-cm) tail, and weigh 26–53 lbs (12–24 kg); females are smaller and much lighter.