The body is streamlined and compressed dorsoventtrally. The snout is a muzzle shape similar to the bill of a duck. Platypuses have a tail shaped like that of a beaver, and webbed fore- and hindfeet.
Males are larger than females.
Range in lengths from 56 cm to 47.5 cm. Prey is taken up by the beak and transferred to the cheek pouches. When diving for food, the platypus fills its lungs with air to utmost capacity so that it may remain underwater for several minutes. The hard parts of crustaceans, insects, and molluscs are ejected into the water by means of a series of horny serrations arranged along the lower jaw. In shallow water, platypuses have been spotted feeding by moving stones aside with their claws, or levering them up with their powerful bills and shoulders to get prey from under the rocks.