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 miters (9,800 feet) deep among extinct volcanoes, they said.

A new species of Marginaster seastar. [Agencies]

The scientists mapped undersea mountains up to 500 miters high and canyons larger than the Grand Canyon for the first time, the government's Commonwealth Scientific and Industrial Research Organization (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 seafloor sampling.

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 miters 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 down there."

Scientists said that only a tiny proportion of Australia's oceans had been explored in such a way and they could only speculate on the biodiversity hidden under the water.

"We have no idea how many species there are, and most of the species we get we only catch once," Bax said.

Environment Minister Peter Garrett described the results as "an amazing day for Australian science".

"It's extraordinary to think that we've put someone on the moon and we're very familiar with lots of parts of the planet, we've got Google Earth and yet here we are, we've got parts of the planet that have never been sighted or explored before," he told national radio.

The minister said the research would help the effort to conserve Australia's ocean biodiversity.

"It'll greatly inform scientists as they deepen their understanding about likely climate change impacts, water currents, and impacts of water temperature on the diversity of species," Garrett said.