Hundreds of new marine species and previously uncharted undersea mountains and canyons have been discovered in the depths of the Southern Ocean, Australian scientists said Wednesday.

A total of 274 species of fish, ancient corals, molluscs, crustaceans and sponges new to science were found in icy waters up to 3,000 metres (9,800 feet) deep among extinct volcanoes, they said.

The scientists mapped undersea mountains up to 500 metres high and canyons larger than the Grand Canyon for the first time, the government's Commonwealth Scientific and Industrial Research Organisation

(CSIRO) said.

The finds were made in marine reserves 100 nautical miles south of the Australian island of Tasmania during two CSIRO voyages in November 2006 and April 2007 using new sonar and video technology as well as seafloorsampling.

Announcing the discoveries in the Tasmanian capital Hobart, CSIRO scientist Kate Wilson said more was known about the surface of Mars than the depths of the world's oceans,

"In Australian waters, for example, more than 40 percent of the creatures brought to the surface by our scientists on a voyage of discovery have never been seen before," she said.

A total of 123 underwater mountains were found, said CSIRO specialist Nic Bax. noting they were home to thousands of deep-sea animals.

"They're really what we call the rainforests of the deep, they provide an area where we get a very' wide range of species collected and that's really unique in the deep sea environment," he said.

In the cold depths of the Southern Ocean "things grow quite slowly so when you're looking at a coral which is maybe two metres high, it may also be 300 years old or more," said Bax.

"So you end up seeing some very old things down there. You can see corals which probably existed 2,000 years ago dowh there."