Amid the discouraging headlines about the extinction of wildlife species around the world, there is this bright spot: So many new species of animals and plants are discovered every year that no one knows the number.

Last week the International Institute for Species Exploration, a scientific group, issued its annual top-10 list of new species and estimated that as many as 18,000 are discovered annually, about half of them insects or arachnids.

The figure has been questioned. Camilo Mora, an assistant professor of geography at the University of Hawaii who has published widely on the subject, said 18,000 is probably too high.

"All of those species are not necessarily new," he said. "They can be corrections of names of species that have two different names, errors like misspellings and so on. After these are accounted for, there are usually about 8,000 a year that turn out to be valid."

But species are fast disappearing, too.

"Loss of habitat is happening on a massive scale," Mora said. "Deforestation, climate change, overexploitation, invasive species — add them together and a number like 20,000 extinctions a year could turn out to be an underestimate."

With thousands of species being identified every year and thousands more going extinct, it might seem that scientists will eventually run out of species to discover. Not so.

In a study published in 2011, Mora calculated that there were 7.4 million to 10 million unnamed plants and animals, not including bacteria and viruses. In other words, 86 percent of land species and 91 percent of marine species are still out there waiting for names. At the pres­ent rate it would take more than 1,000 years to catalog them all.

In releasing the top-10 list of newly discovered species, the exploration institute’s director, Quentin D. Wheeler, acknowledged that it was not a scientific proj­ect but added that its purpose was serious.

"We want to achieve awareness of the biodiversity crisis," said Wheeler, an entomologist who is president of the State University of New York College of Environmental Science and Forestry, in Syracuse. "If we don’t know where species are, we can’t detect invasive species or measure rates of extinction. If we don’t know what’s there to begin with, we can’t make the right calls."

Nicholas Bakalar, New York Times

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