What are the 3 mammals that lay eggs?

There are only three egg-laying mammals, which are known as monotremes: the platypus, the short-beaked echidna and the long-beaked echidna.

There are three sub-species of the long-beaked echidna: the Western long-beaked echidna, Sir David's long-beaked echidna and the Eastern long-beaked echidna.