Many of the species were found in the so-called Heart of Borneo, a thickly forested mountainous region covering around 220,000 square kilometers (85,000 square miles) in the centre of the island.

The finds include the world's second smallest vertebrate, a tiny species of fish that measures less than one centimetre (1.25 inches) in length and thrives in the island's highly acidic blackwater peat swamps.

There is also a catfish with a protruding teeth "and an adhesive belly which allows it to literally stick to rocks," as well as six species of Siamese fighting fish, including one species with a gorgeous iridescent blue-green colouring.

The 52 new species have been covered in the past year alone.

In February, scientists said they had had found a "Garden of Eden" in the Foja Mountains, on the island of New Guinea, where they recorded dozens of new species of butterflies, frogs, palms and rhododendrons.

They also found a unique local species of honeyeater bird -- the first new bird to be sighted on New Guinea for more than 60 years -- and determined that the mountains were the home of one of the most elusive bird species of all, a creature called the Berlepsch's bird of paradise.

WWF said many more species waited to be discovered in Borneo, which is divided between Brunei, Indonesia and Malaysia, but expressed deep concern about the loss of equatorial rainforest, which is being cleared for rubber, oil palm and pulp production.

"The more we look, the more we find," said Stuart Chapman, international coordinator for WWF's Heart of Borneo programme. "These discoveries reaffirm Borneo's position as one of the most important centres of biodiversity in the world."

Related Links
WWF Heart of Borneo Programme
Darwin Today At TerraDaily.com