Kloss's gibbon, also known as the Mentawai gibbon, the bilou or the dwarf siamang, is a primate in the gibbon family. It is all black, resembling the siamang but considerably smaller and lacking the siamang's distinctive throat pouch. It reaches 43–64 cm and weighs at most about 5.9 kg. Like all gibbons it has long arms and no tail, and males and females are difficult to tell apart (Wikipedia, general species account).
Description: Wildlife of Sumatra guide, Wildlife of Everywhere (wildlifeofeverywhere.com); general species information paraphrased from Wikipedia (CC BY-SA)
Mammals of the World