There are actually about 265 species of monkeys, which does not include apes. Monkeys are pretty intelligent, and one thing that separates them from other primates is the fact that they have tails.
Tails are an interesting topic in and of itself because they are not actually limited to being on animals. An air plane for example also has a tail.
How many types of airplanes are there? And how many do not have a tail?