The white-cheeked spider monkey (Ateles marginatus) is a species of spider monkey, a type of New World monkey, endemic to Brazil.There are many different varieties of spider monkeys that make their home in the upper levels of the rain forest. The white-cheeked spider monkey was placed on the endangered species list after an assessment in 2008 discovered that their population had decreased by 50% over the course of three generations; this decline can be attributed to habitat loss and hunting.