The estimated number of animals and plants on our blue planet described and classified by Biologists is about 1.7 million ( 2010 ) and this is less than one quarter of the total species estimated or yet to be discovered and described . Every year scientists record about 18,000 new species of plants and animals . Out of this approximately 13,500 are new invertebrates . So far 1,305,250 invertebrates have been discovered , and so many species are waiting to be described . Between 1999 and 2009 more than 1,200 new species of plants and animals were discovered in " Amazone " . Details of newly discovered species can be obtained by visiting following websites :
http://wwf.panda.org -World Wildlife Foundation
zsí.gov.in -Zoological Survey of India
http://news.mongabay.com -Also gives information on newly discovered species
www.zsi.com -Zoological Society of Land
www.wes.org -World Conservation Society
http://species.asu.edu -International Institute for Species Exploration
http://indianbiodiversitytalk.biogspot.in
www.wii.gov.in -Wildlife Institute of India .
As evident from above a large number of animals inhabit the earth today and many more have lived here in the past and equally more are waiting to be listed . These animals vary in their shape and size , habit and habitat , colour , form and weight as well as in their distribution . The nanobes are the smallest living organisms known on the earth . They were discovered in ocean by Dr. Phillipa Uwins , from Queensland University ( Australia ) during an oil drill in 1991. The nanobes have a length of 20 to 150 nanometers ( the millionth part of a meter ) . They are almost a thousand times smaller than the smallest cells in our body and ten times smaller than the smallest known bacterium . While Blue whale ( Balaenoptera musculus ) is the largest animal weighing 100-200 tonns and measuring 25-30 meters in length . There are few animals which are different from what they look like . For instance , a bat which looks like a bird is not really a bird but is a mammal like a man . Likewise a whale which generally known as a fish is not a fish . These things appear to be surprising to a common man . A considerable part of animal kingdom on one hand is so small in size that they can only be observed with the help of a microscope and many of them live in water . On the other hand giant sized animals like Elephant , Rhino , Hippo live on the earth . Animals of all kinds i.e. , round , flat , elongated , fat , colourful as well as scary in shape and size exist in nature . There are certain animals which are known only by fossil remains . Diversity amongst animals does not exist in their shape and size only but also in their species , number and habitat . Starting from the indefinitely deep vents in oceans to snow covered mountain peaks and from the poles of the earth to the equator , the animals inhabit all the places . From the point of view of habits and habitat some animals live in fresh water ponds and rivers . The animals living in flowing water in a river are called lotic and those inhabiting the stagnant water of ponds , pools , lakes and swamps , are called lentic . Amongst the marine animals , a few living near the water surface are pelagic , those living in the depths of the oceanic water are abyssal . A few others living near the oceanic bottom are littoral and still other leading a sedentary life on the sea - bottom are benthic . In the same way some animals living under the surface of the earth are subterranean , others inhabiting the earth surface are terrestrial . some of them living on trees are arboreal and still others flying in air are aerial . The fast runners on the earth are cursorial while with digging habit are called fossorial animals . Therefore it is clear that with this great diversity of animals their study is not so easy . There are water areas where big rivers join the ocean , called estuarine water and have lesser salinity than sea water . A few fishes are unable to survive throughout their life in marine water as for example salmon and trouts . These fishes come for spawning to the estuaries and are called anadromous fishes in contrast to those which migrate from the estuaries to the sea for the purpose of spawning are called catadromous fishes like fresh water eels . Based the salanity tolerance the fishes euryhaline , migrating between fresh estuaries and salt water and have wide salinity tolerance . On the other hand fishes having a narrow range of salinity tolerance remain confined either to fresh water or salt water are called stenohaline .
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