Echidnas

The echidna is a monotreme, an unusual mammal that actually lays eggs. The eggs incubate in the mother's pouch for about 10 days, then, after hatching, live in the pouch for 7-8 weeks suckling their mother's milk. The milk is secreted from pores in the pouch, the female has no nipples. Now the baby leaves the pouch, and is left in a burrow while the mother looks for food.
The echidna doesn't cope well with temperature extremes, and so spends most of its time in hollow logs or under a thick bush or debris. They has no sweat glands, so keeping cool is important. In winter they may semi-hibernate, lowering their body temperature to 12 degrees Celsius and going into a deep sleep for 10 or more days to conserve energy.
If an echidna feels threatened, it quickly digs into the dirt, camouflaging itself. Sometimes the ground is too hard to dig, and then the echidna will curl into a ball, and its spines protect it.
The spines are made of keratin (like your nails), and are sharp. The underside of the echidna is soft skin, and babies don't grow spines until they leave the pouch.
Echidnas live almost anywhere in Australia, from the tropical north to the temperate south. An interesting fact is that northern echidnas have more spines and less fur, while southern echidnas have more fur and less spines.