Which primate uses its tail as a fifth limb?

The primate that uses its tail as a fifth limb is the spider monkey.

Spider monkeys are New World monkeys in the genus Ateles, native to tropical forests of Central and South America. Their long, muscular, prehensile tails have a hairless gripping tip and can support the animal’s weight. This tail acts much like an extra hand, helping the monkey hang, balance, climb, and reach fruit high in the rainforest canopy.

Their other body adaptations fit the same lifestyle. Spider monkeys have long arms, hook-like fingers, and greatly reduced or absent thumbs. These features help them swing beneath branches in a form of movement called brachiation. They spend much of their time in the upper canopy, where returning to the ground can be risky.

Howler monkeys also belong to a family of New World monkeys with prehensile tails, so the wording can sound broader than it is. Among the listed choices, however, spider monkey is the clear canonical answer. The famous “fifth limb” description is especially associated with spider monkeys’ powerful, flexible tails.