Answer:
Yes: specifically, it is a monotreme, which is an egg-laying mammal.
The only other species which is an egg-laying mammal is the echidna.
A platypus is a mammal because the young feed on milk produced in the mother's mammary glands. It also has fur, is warm-blooded and breathes through lungs, like other mammals.
A platypus is a egg-laying mammal that lives in lakes and streams.