The platypus’s general appearance is quite distinctive, combining a streamlined, furry body with a broad, paddle-shaped tail, four short legs, and a superficially ducklike bill. To help reduce drag in the water, the male’s testes and penis are normally held within the body. A platypus also lacks ear flaps (or pinnae): the ear and eye are both located in a muscular groove placed at the side of the head, which automatically pinches shut when an animal dives to protect the eye and ear underwater.

The platypus’s body is covered by dense fur apart from its bill, feet and tail. The bill is covered by smooth skin with a soft, suede-like texture and (unlike a duck bill) is quite pliable and fleshy around the edges. The upper surface of the tail is covered by coarse hairs which can stand up to the wear and tear involved in using the tail to help push aside and tamp down soil when a platypus digs or remodels a burrow (see 1.3.5, Burrows ). In contrast, the tail’s lower surface is covered by short, fine hairs which are replaced each year when an animal moults but then wear away as the tail is dragged over stones and gravel, leaving the tail mostly bald below.

Across their entire range, platypus is dark brown above (except for a small patch of light-coloured fur located next to each eye) and creamy white below (sometimes tinged rusty-red). When the platypus’s eyes are closed underwater, the light-coloured patches give the appearance of eyes remaining open, presumably fooling predators into being less likely to attack.

The upper surface of the bill is uniformly dark grey, with two nostrils located near the tip. The bill’s lower surface can either be uniformly pigmented or quite mottled.

The platypus’s front foot is furnished with a broad expanse of skin which extends past the front claws to form a large and efficient paddle (below left). The webbing folds under the foot when out of the water, making it easier for a platypus to walk and use the sturdy front claws to dig burrows. The hind feet are used to help change direction and maintain balance in the water. In addition, they are equipped with sharp, curved claws used to groom the fur (below right).

Like many other animals, platypus living at the warm end of their range in Queensland is generally somewhat smaller than those found at the cold end of their range in Victoria and Tasmania. The largest platypus recorded to date (in Tasmania) was a male weighing 3.0 kilograms and measuring 0.6 metres in length. On the mainland, adult males typically weigh 1.2-2.4 kilograms and are on average 0.5 metres long, whereas adult females typically weigh 0.7-1.6 kilograms and are on average 0.4 metres long.

Further reading:
Connolly, J.H. and Obendorf, D.L. (1998). Distribution, captures and physical characteristics of the platypus (Ornithorhynchus anatinus) in Tasmania. Australian Mammalogy 20: 231-237.

Grant, T.R. and Temple-Smith, P.D. (1983). Size, seasonal weight change and growth in platypuses, Ornithorhynchus anatinus (Monotremata: Ornithorhynchidae), from rivers and lakes of New South Wales. Australian Mammalogy 6: 51-60.