Final answer:
The total number of named and unnamed species in Australia is estimated to be roughly 600,000, with 500,000 being the closest choice provided. This number reflects both described and predicted species across various forms of life, including plants and insects like beetles.
Step-by-step explanation:
According to Numbers of Living Species in Australia and the World, a report by A.D. Chapman, the estimate for the total number of species in Australia, including both named and as yet undescribed species, is approximately 600,000. Specifically, there are about 147,579 named species and a further 447,408 species that have been estimated but not yet described, leading to a combined total of roughly 595,000 species. Therefore, among the choices provided, the correct answer would be 500,000 named and unnamed species in Australia, which is acknowledged as a conservative number, considering ongoing discoveries in biodiversity.
This total encompasses a vast diversity of life forms, from mammals and birds to insects like beetles—of which there are about 350,000 species—and plants such as orchids, with approximately 30,000 species globally. The discovery and description of new species continue to this day, and while some groups have seen a decline in new species identification over time, others, particularly plants, have seen the numbers rise with the advent of modern taxonomic techniques.