Geoffroys spider monkey mother (Ateles geoffroyi) with baby. These monkeys have arms that are considerably longer than their legs and their prehensile tail serves as an extra limb. While their hands have only a rudimentary thumb, their fingers are long, strong, and hook-like. These physical traits allow the spider monkey to move by swinging beneath tree branches. Photographed in Puerto Barillas, Jiquilisco Bay, El Salvador.