Gibbons, specifically the Siamang (Symphalangus syndactylus), are a robustly built species among the 10 other species in the family Hylobatidae. Measuring 75-90 cm (29.5-35.4 in) long and weighing 8-13 kg (17.6-28.6 lbs), S. syndactylus possesses an arm-spread of 1.5 m (almost 5 ft). S. syndactylus is black in color with a longer, thinner coat than other species. The Siamang is distinguished by a large, hairless, empty air sac on the front of their throats that inflates during vocalization, and by webbing between their second and third toes. S.