What do they look like?
About half the size of a household cat, adult males and females can differ greatly in size and weight. The average male platypus is about 50 centimetres long (head to tail) while females measure about 43 centimetres.
Platypuses are dark brown on their backs and generally light brown on their bellies. Under their long, coarse outer hair is a fine, dense underfur which is woolly in texture. This fur ranges in colour from grey to dark brown.
With their slightly flattened, streamlined body and short, stout legs, they are well-adapted for swimming. The forelegs push the animal through the water, while the hind legs trail behind, acting as stability rudders. When digging a burrow or moving on land, platypuses can fold away their webbed foot extensions. The name 'platypus' means 'flat feet'.
The platypus has no outer ear lobe, and both its eyes and ears close when it dives. It has very sharp vision over long distances, but because its eyes are towards the top of its head it cannot see objects directly under its nose.
The duck-like bill of the platypus is a flexible, soft and very sensitive organ. It helps the animal to find its way, to search for food and to pick up electrical discharges from its prey. Although it has no teeth, the platypus uses grinding plates on the upper and lower surfaces of the jaw to chew its food.
The platypus keeps its body temperature constant by controlling the heat produced from metabolism (all the chemical reactions that occur in the body). It can reduce blood flow to areas of its body that have no fur - particularly its tail, rear feet and bill. Its fur is waterproof and traps an insulating layer of air next to its skin.
Did you know?
The platypus and two species of echidna are the world's only monotremes, or egg-laying mammals.
The name 'monotreme' comes from the fact that these animals have only a single opening for reproduction and getting rid of body wastes.
When the first platypus specimen was sent to England for identification, its appearance was so strange that it was thought to be a hoax. An animal that had a muzzle like a duck's bill and carried a tail like a beaver was said to be an impossibility.
Since then, scientists have come to accept that this Australian native is very real. But it's something of a rarity.
Platypuses are shy animals, and will usually dive underwater to swim away from an attacker. However, if unable to escape, male platypuses will try to stab an attacker with the hollow spurs on their hind legs. These spurs are connected to a sac containing poison strong enough to kill a dog.