Geoffroy's spider monkey (Ateles geoffroyi), also known as the black-handed spider monkey or the Central American spider monkey, is a species of spider monkey, a type of New World monkey, from Central America, parts of Mexico and possibly a small portion of Colombia. There are at least five subspecies. Some primatologists classify the black-headed spider monkey (A. fusciceps), found in Panama, Colombia, and Ecuador as the same species as Geoffroy's spider monkey. It is one of the largest New World monkeys, often weighing as much as . Its arms are significantly longer than its legs, and its prehensile tail can support the entire weight of the monkey and is used as an extra limb. Its hands have only a vestigial thumb, but long, strong, hook-like fingers. These adaptations allow the monkey to move by swinging by its arms beneath the tree branches. Geoffroy's spider monkey lives in fission–fusion societies that contain between 20 and 42 members. Its diet consists primarily of ripe fruit and it requires large tracts of forest to survive. As a result of habitat loss, hunting and capture for the pet trade, it is considered to be endangered by the IUCN. Taxonomy Geoffroy's spider monkey belongs to the New World monkey family Atelidae, which contains the spider monkeys, woolly monkeys, muriquis and howler monkeys. It is a member of the subfamily Atelinae, which includes the spider monkeys, woolly monkeys and muriquis, and of the genus Ateles, which contains all the spider monkeys. The genus name Ateles means "imperfect", a reference to the vestigial thumb. The species name geoffroyi is in honor of French naturalist Étienne Geoffroy Saint-Hilaire. Agreement over the number of spider monkey species is not universal. Kellogg and Goldman (1944) based their classification on fur color, and Groves (1989) based his on fur color and geographic distribution. Kellogg and Goldman differentiated Geoffroy's spider monkey from other species by its dark black head, hands and wrists. Recent studies use mitochondrial DNA to help differentiate species. Such studies by Collins and Daubach (2000, 2001, 2006) indicate the Geoffroy's spider monkey is more closely related to the white-fronted spider monkey, A. belzebuth, and the brown spider monkey, A. hybridus, than it is to the red-faced spider monkey, A. paniscus. According to these studies, A. paniscus branched off from the other spider monkeys approximately 3.27 million years ago and the spider monkeys branched off from the woolly monkeys and