The video of a strange creature found by a fisherman in the sea of Vietnam has gone around the world through the web. It has aroused a lot of curiosity and also provoked ironic comments about the ease of spreading false news. The news of sightings of unknown animals are frequent and thanks to the web circulate immediately. A few months ago in Australia people found the carcass of an animal on the beach. It could be a dolphin, or a whale, or a crocodile. In most cases, however, these sightings of unknown creatures are denied by the investigations of scientists.
No one knows exactly how many species there are on Earth. According to a 2011 study published in the scientific journal Plos there are about 8 million and 750 thousand. The estimate takes into account only those eukaryotes, i.e. formed by cells with nuclei. The calculation was carried out by a group of marine ecologists from the universities of Hawaii and Dalhousie University in Halifax, Canada. The majority, 6.5 million species, would live on Earth and the rest, 2.2 million species, in the Oceans. Animals would represent the majority of species (but not of individuals) with 7.7 million. Among the animals, those that show the greatest variety are insects, followed by spiders.
Scientists themselves report a possible margin of error of 1.3 million more or less species. In any case, this new estimate greatly reduces uncertainty about what the biologists thought. The accredited hypothesis, in fact, was that the existing species could be between 3 and 100 million. Another research, published last year by The Quarterly Review of Biology, counts instead of two billion species. In this case, however, the species of bacteria, which are estimated to be many more, are not considered. Moreover, scientists do not consider the species already extinct, which still represent the majority of the types of living beings that have populated the planet.
If the lowest estimate of 8.3 million were true, the number of known species would still represent only 15% of the total. For every plant or animal or other living thing that humans have seen at least once and named, there would be at least six more that are still unknown.
The discovery of new species continues unabated, but even in this case it is difficult to get precise numbers. A few months ago an expedition from Oxford University announced the discovery of over 100 new marine species in the waters of Bermuda. A WWF report lists 381 new species found in the forests of the Amazon over two years. These range from mammals to insects, reptiles, birds and plants.
Scientists have calculated that, at the rate at which the discoveries occurred in the last 250 years, it would take another 480 years to complete the list. Meanwhile, many species may have become extinct before they are ever detected by humans.