Humans are sharing planet Earth with some 8.7 million different species, though a small number of them have been discovered and catalogues, researchers revealed on Tuesday.

This census is being called the most precise calculation ever offered and is presented in the journal PLoS Biology. It replaces previous estimates that hovered between three million and 100 million.

There are 1.2 million species officially registered in the Catalogue of Life and the World Register of Marine Species. Swedish scientist Carl Linnaeus came up in the mid-1700s with the taxonomy system still used today.

The new figure of 8.7 million is a projection based on a mathematical analysis of currently known species.

According to Discovery News, the researchers discovered numerical relationships between the higher levels of taxonomic division, like order and phylum, and the number of species. They used these patterns and were able to make a more realistic estimate of species numbers.

We discovered that, using numbers from the higher taxonomic groups, we can predict the number of species, said Sina Adl, one of the co-authors of the study, to Discovery News. The approach accurately predicted the number of species in several well-studied groups such as mammals, fishes and birds, providing confidence in the method.

The findings by scientists at Dalhousie University in Canada and the University of Hawaii stated that approximately 86 percent of land species and 91 percent of creatures in the ocean have yet to be discovered.

The question of how many species exist has intrigued scientists for centuries and the answer, coupled with research by others into species' distribution and abundance, is particularly important now because a host of human activities and influences are accelerating the rate of extinctions, lead author Camilo Mora of the University of Hawaii told Agence France-Presse. Many species may vanish before we even know of their existence, of their unique niche and function in ecosystems, and of their potential contribution to improved human well-being.

The study estimated that there are 7.77 million species of animals, of which 953,434 have been described and catalogued. So far, there are about 298,000 species of plants, with 215,644 of them described and catalogued.

Researchers also said there are possibly 611,000 species of fungi, of which 43,271 are known to science.

Moreover, 36,400 species of protozoa, or single-cell organisms such as amoebas and 27,500 species of chromista, such as brown algae and water molds, were also included in the projected count.

We have only begun to uncover the tremendous variety of life around us, co-author Alastair Simpson told Discovery News. The richest environments for prospecting new species are thought to be coral reefs, seafloor mud and moist tropical soils. But smaller life forms are not well known anywhere. Some unknown species are living in our own backyards ? literally.

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