The Siamang is an arboreal black furred gibbon native to the forests of Malaysia and Sumatra. The largest of the lesser apes, the siamang can be twice the size of other gibbons, reaching 100cm in height, and weighing up to 23kg.

The siamang is distinctive for two reasons. The first is the fact that two fingers on each hand are fused together (hence the name "syndactylus"). The second is the large "gular sac", a throat pouch which can be inflated to the size of the head, allowing siamangs to make loud resonating calls.

Siamangs can live up to 20 years in captivity.