apes)
** Yet to be classified: other New World monkeys (tamarins, Aotidae: night or owl monkeys, Pitheciidae: titis, sakis and uakaris, Atelidae: howler and woolly monkeys)

The spider monkey compensates for being virtually thumbless by using the hairless part of its long, prehensile tail for grabbing objects. In apes and Old World monkeys, the thumb can be rotated around its axis, but