They do not present sexual dirmorphism (differences between males and females) in size neither in dentition, only in coloration in the first two genera of the 4 existing ones: Nomascus, Hoolock, Hylobates and Symphalangus.
The intermembral index (length of upper extremities/lower ext*100) is the highest of all primates: 127-147.
They are the only apes with ischial callosities (a hardening of the tissue covering the back of the pelvis, related to the way they sleep: seated).
Among today’s apes, they are the smallest, the most diverse (largest number of species) and the most numerous (although they are endangered).
They live in tropical forests of Southeast Asia.
They are strictly arboreal, but bipeds if they go down to the ground or if they go by horizontal big branches. Very agile and almost strict brachiators.
Their vocalizations are very intense (they can be heard at Km) and vary depending on the context, the species, each individual… The frequency at which they emit varies between 0.2 and 5kHz.