Platypus

The platypus is an egg laying mammal that is well adapted to the water. Physically, it looks like a mole or otter, with a beaver's flattened tail and a duck's bill. It also has short, powerful legs and webbed feet. While the fur on its back is dense, bristly, and reddish or blackish brown, the fur on its underbelly is soft and gray. Its eyes are very small, and it does not have external ears. The platypus measures around 17.7 in (45 cm) in length, with its tail adding an additional 5.9 in (15 cm). Commonly referred to as the duck-billed platypus, it spends several hours each day in the creeks and rivers of eastern Australia and Tasmania. The rest of its time is spent in burrows, which it digs in the river banks.

The platypus is classified in the order Monotremata (meaning single hole), consisting of two families and three genera; the families are Tachyglossidae (spiny anteater family) and Ornithorhynchidae (platypus family). There is only one species of platypus, Ornithorhynchus anatinus, which is comprised of four subspecies. All three species in the order Monotremata are considered primitive, combining mammalian features with those of lower orders of vertebrates such as reptiles. For example, monotremes are the only egg-laying mammals. In other mammals, the young are conceived within the female's body and are born alive. In monotremes, the eggs are fertilized internally, but are incubated and hatched outside the body. Monotremes, like all reptiles, also have a cloaca, a single opening through which feces, urine, and sperm or eggs pass. In other mammals, the cloaca is divided into an anus and genitourinary passages. Like other mammals, monotremes have fur, nurse their young with milk, and are warm-blooded.