Fauna of Australia species are nocturnal and many arboreal. Two of the five living species of monotreme occur in Australia: the platypus and the short-beaked echidna. The monotremes differ from other mammals in their methods of reproduction; in particular, they lay eggs instead of giving birth to live young. The platypus—a venomous, egg-laying, duck-billed amphibious mammal—is considered to be one of the strangest creatures in the animal kingdom. When it was first presented by Joseph Banks to English naturalists it was thought to be so strange that it was a cleverly created hoax. The short-beaked echidna is similarly strange, covered in hairy spikes
Monotreme nipples. All five extant species show prolonged parental care of infants, with low rates of reproduction and relatively long life-spans. Monotremes are also noteworthy in their zygotic development. Most mammal zygotes go through holoblastic cleavage, meaning that after fertilization, the ovum splits into multiple, divisible daughter cells. In contrast, the zygotes of monotremes, like those of birds and reptiles, undergo meroblastic (partial) division. This means the cells at the yolk's edge have cytoplasm continuous with that of the egg, which allows the yolk and embryo to exchange waste and nutrients with the surrounding cytoplasm. Monotremes' metabolic rate is remarkably low