How many animals have a blowhole?

Whales, dolphins and porpoises have a blowhole, (or nostrils), on top of their head so they can breathe in and out when they are on the surface of the water.

Since they are the only mammals that spend their entire lives in the water, and much of it underneath the surface, they are the only mammals to have a blowhole on top of their head. Most mammals have their nostrils in the front of their face, similar to human beings.