~1.4 million species
||Régnier C et al., Mass extinction in poorly known taxa. Proc Natl Acad Sci U S A. 2015 Jun 23 112(25):7761-6. doi: 10.1073/pnas.1502350112 p.7761 left column bottom paragraphPubMed ID26056308
|| Chapman AD (2009) Number of Living Species in Australia and the World. Report for the Australian Biological Resources Study (Department of the Environment, Water, Heritage and the Arts of the Australian Government, Canberra, Australia)
||Abstract: "Here [investigators] show, based on extrapolation from a random sample of land snail species via two independent approaches, that we may already have lost 7% (130,000 extinctions) of the species on Earth."
||P.7761 left column bottom paragraph: "Only 15,911 invertebrate species of ∼1.4 million described (primary source) are listed by IUCN. Of these, only 28% are categorized as data deficient, a proportion that may seem low (i.e., the conservation status of almost three-quarters of the invertebrate species evaluated could indeed be assessed)."