What mammal swims like a fish and has a duck beak?

The platypus, one of only two types of mammals that lay eggs, has a duck-like bill, or extended snout, which is not actually a beak. The animal was commonly referred to as the duck-billed platypus.

The bill does not open as a bird's beak does, the mouth being on the underside and the nostrils on the front of the upper side.