Original sentence: They are generally identified by convention rather than any strict criteria, but seven areas are commonly reckoned as continents – they are (in descending order of size): Asia, Africa, North America, South America, Antarctica, Europe, and Australia
Edited sentence: They are generally identified by convention rather than any strict criteria, but six areas are commonly reckoned as continents – they are (in descending order of size): Asia, Africa, America (subdivided in North America, Central America and South America), Antarctica, Europe, and Oceania (including Australia)