Continent world ultimately persisted with these being regarded as separate continents. From the late 18th century, some geographers started to regard North America and South America as two parts of the world, making five parts in total. Overall though, the fourfold division prevailed well into the 19th century. Europeans discovered Australia in 1606, but for some time it was taken as part of Asia. By the late 18th century, some geographers considered it a continent in its own right, making it the sixth (or fifth for those still taking America as a single continent). In 1813, Samuel Butler wrote of Australia
Smallest organisms that lives between sand grains on the coast of India. Its maximum length is only 4 mm. The smallest sea urchin, "Echinocyamus scaber", has a test only 6 mm across. "Patiriella parvivipara" is the smallest starfish, at only 5 mm across. The smallest vertebrates (and smallest amphibians) known are "Paedophryne amauensis" frogs from Papua New Guinea, which range in length from , and average . Previously, the title of smallest vertebrate was held by members of the fish genus "Paedocypris" of Indonesia. The one of world's smallest fish based on the minimum size at maturity is "Paedocypris progenetica" from Indonesia,