Siamangs are the largest and darkest of the gibbon species and are well suited for life in a forest’s treetops. Yet there are some features on their hands and feet that make siamangs different from other gibbons. They have four long fingers and a smaller opposable thumb on their hands, and their feet have five toes, with an opposable big toe. That means siamangs can grasp and carry things with both their hands and their feet. The opposable thumb and toe aren’t found in other members of the gibbon family.