Most primates have opposable thumbs that that help them grasp and manipulate objects. However, the spider monkey, Ateles geoffroyi, is one exception in which their hands have no thumbs at all! Instead, spider monkeys have a specialized prehensile (grasping) tail that is hairless on its underside and has a fleshy pad that is unique to each monkey (like a fingerprint). Spider monkeys are arboreal (meaning they spent most time up in trees), they use their long arms and prehensile tails to move from tree to tree.

Sketch and fact contributed by Nalina Aiempichitkijkarn

Source: https://www.birminghamzoo.com/animal/black-handed-spider-monkey/