Hylobates klossii, commonly known as Kloss's gibbon, is a species of gibbon found exclusively on the Indonesian island of Sumatra. These small primates are known for their long arms and distinctive vocalizations, which they use to communicate with one another. Kloss's gibbons have a unique black fur coat, with some individuals displaying a white or cream-colored face. This species primarily inhabits tropical rainforests, where they spend most of their time in trees. Kloss's gibbons are arboreal and are known for their impressive swinging abilities, allowing them to move swiftly through the canopy. They are also considered endangered due to habitat loss and hunting.