Platypus, monotreme mammal of Australia and Tasmania. It is amphibious, choosing to live in lakes and streams. It lays eggs and has webbed feet, a broad tail and a soft duck-like bill. The male has a poison spur on the hind foot, which is used in courtship combats and is highly poisonous to man. It is 60cm long and eats small invertebrates. Family Ornithorhynchidae; species Ornithorhynchus anatinus.