Order Monotremata: Egg-laying Mammals
The monotremes are distinguished from the placental mammals (or eutherian mammals) in the way they reproduce. Monotremes are the only mammals that are oviparous (egg layers).
There are only a few types of monotremes: the Duck-billed platypus, the short-billed echidna, and the long-billed echidna.
The name Monotremata means “one opening” and refers to the cloaca, a common opening for the fecal, urinary, and reproductive tracts.