Platypus

The platypus is a semiaquatic animal, and many of its physical characteristics are adaptations for its life as a fresh-water predator. Its legs are short but powerful, and the feet are webbed, though the digits retain large claws, useful for burrowing. On the forefeet the webs extend beyond the claws and make efficient paddles; on land, the webs can be folded back to free the claws for digging. On each ankle the male platypus has a spur connected to poison glands in the thighs; these spurs are used against an attacker or against a competing platypus but never against prey. The poison is not fatal to man but causes intense pain.  The platypus's eye and ear openings lie in furrows which are closed off by folds of skin when the animal is submerged. Thus, when hunting underwater, the platypus relies on the sensitivity of its tactile, leathery bill to find prey. The nostrils are toward the end of the upper bill but can only function when the head is in air. Young platypuses have teeth, but adults have horny, ridged plates on both sides of the jaws for crushing prey.

The platypus feeds mainly at the bottom of the water, making dives lasting a minute or more to probe the mud with its bill for crustaceans, aquatic insects and larvae. It also feeds on frogs and other small animals and on some plants. Platypuses have huge appetites, consuming up to 1 kg (2 1/4 lb) of food each night.  Short burrows dug in the riverbank above the water level are used by the platypus for refuge or during periods of cool weather. In the breeding season, however, the female digs a burrow 12 m (40 ft) or more in length, at the end of which she lays her 2 or 3 eggs on a nest of dry grass and leaves; the rubbery eggs are cemented together in a raft. She plugs the entrance to the burrow with moist plant matter, and this prevents the eggs from drying out during the 7-to 14-day incubation period. When the young hatch, they are only about 1.25 cm (1/2 in) long and helpless. Until they are about 5 months old, they feed on milk, which issues from slits in the mother's abdominal wall. Unlike spiny anteaters, they do not draw up tucks of skin into pseudonipples but lap and suck the milk off their mother's abdominal fur.