An anaconda as long as a limousine, a giant catfish that eats monkeys, a blue-fanged spider and poisoned dart frogs are among the 1,220 animals and plants to have been found from 1999 to 2009, according to the study.
The report was released on the sidelines of a United Nations summit in Japan that is being held to try to stem the mass extinction of species around the world, and the WWF said it highlighted why protecting the Amazon was so vital.
“This report clearly shows the incredible, amazing diversity of life in the Amazon,” Francisco Ruiz, head of WWF’s Living Amazon Initiative, told reporters at the launch.
“[But] this incredible region is under pressure because of the human presence. The landscape is being very quickly transformed.”
Logging and clearing for agricultural uses such as cattle farming and palm oil plantations have led to 17% of the Amazon — an area twice the size of Spain — being destroyed over the past 50 years, according to the WWF.
One of the most amazing discoveries was a four-metre (13ft) anaconda in the flood plains of Bolivia’s Pando province in 2002.
It was the first new anaconda species identified since 1936 and became only the fourth known type of that reptile, according to the WWF.
There were a total of 55 reptile species discovered, with others including two members of Elapidae — the most venomous snake family in the world that includes cobras and taipans.
A kaleidoscope of different-coloured frogs were also found, including 24 of the famed poison dart variety and one that was translucent.
Among the 257 types of fish discovered in the rivers and lakes of the Amazon was a “goliath” catfish.
One of them found in Venezuela measured nearly 1.5 metres long and weighed 32kg (over 70lb).
Although the “goliath” catfish normally exists on a diet of other fish, some of them have been caught with parts of monkeys in their stomachs, according to the WWF.
Another extraordinary species of catfish that was discovered in the Brazilian state of Rondonia was extremely small, blind and red.
Villagers found the fish when they accidentally trapped them in buckets after hauling up water from a well.
At least 500 spiders were also discovered, including one that was completely brown except for a pair of almost fluorescent blue fangs.
Thirty-nine new mammals were also found, including a pink river dolphin, seven types of monkey and two porcupines.
Among the 637 new plant species discovered were sunflowers, ivy, lilies, a variety of pineapple and a custard apple.
The Amazon is home to at least 40,000 plant species, and the WWF described the scale of diversity in some areas as “mind-boggling”.
It said 1,000 plant species were documented in one hectare (2.5 acres) of lowland rainforest in Ecuador, while 3,000 were found in a 24-hectare region of the Colombian section of the Amazon.
As part of efforts to save the Amazon, the Brazilian government has worked with the WWF, the World Bank and other groups to establish protected areas of rainforest covering 32 million hectares over the past six years.
The WWF said the protection efforts — in which foreign governments and organisations provide some of the finance to help run the projects — should serve as a model for the whole world in how to save rainforests.