A platypus is a mammal. However, it's an unusual mammal in that it lays eggs. This makes it a monotreme as well as a mammal. It's also an aquatic creature that has a bill that resembles a duck's. The males have spurs on their back legs that produce venom.
The female platypus gestates her eggs for about 27 days. Once they're laid, they take between six and 10 days to hatch. They are round and leathery like reptile eggs. Like some other mammals, platypus females produce milk but have no nipples. Baby platypuses have to lap the milk from the mother's abdomen. They are nursed for about three or four months.