Bangkok, Thailand - The polar oceans are not biological deserts after all.

A marine census released Monday documented 7,500 species in the Antarctic and 5,500 in the Arctic, including several hundred that researchers believe could be new to science.

"The textbooks have said there is less diversity at the poles than the tropics, but we found astonishing richness of marine life in the Antarctic and Arctic oceans," said Victoria Wadley, a researcher from the Australian Antarctic Division who took part in the Antarctic survey. "We are rewriting the textbooks."

In one of the biggest surprises, researchers said they discovered dozens of species common to both polar seas - separated by nearly 7,000 miles (11,000 kilometers). Now they have to figure out how they separated.

"We probably know more about deep space than we do about the deep polar oceans in our own backyard," said Gilly Llewellyn, leader of the oceans program for the environmental group WWF-Australia. She did not take part in the survey. "This critical research is helping reveal the amazing biodiversity of the polar regions."

Most of the new discoveries were simpler life forms known as invertebrates, or animals without backbones.

Researchers found scores of sea spider species that were as big as a human hand, and tiny, shrimp-like crustaceans in the Arctic basin that live at a depth of 9,850 feet (3,000 meters).

The survey is one of several projects of the Census of Marine Life, an international effort to catalog all life in the oceans. The 10-year census, scheduled for final publication in 2010, is supported by governments, divisions of the United Nations and private conservation organizations.

The survey - which included over 500 polar researchers from 25 countries - took place during International Polar Year which ran in 2007-2008.

Researchers endured up to 48-foot (16-meter) waves on their trip to the Antarctic, while their colleagues in the Arctic worked under the watchful eye of a security guard hired to protect them from polar bears.

New technology also helped make the expeditions more efficient and productive than in the past. Researchers used cell-phone-like tracking devices to record the Arctic migration of narwhals, a whale with a long twisted tooth, and remotely operated submersibles to reach several miles (kilometers) down into the oceans to study delicate marine animals that are impossible to collect.

As many as 235 species were found in both polar seas, including five whale species, six sea birds and nearly 100 species of crustaceans.

"We think of the Arctic and Antarctic as similar habitats but they are separated by great distances," said University of Alaska Fairbanks plankton ecologist Russ Hopcroft, who took part in the Arctic survey.

"So finding species at both ends of the Earth - some of which don't have a known connection in between - raises a whole bunch of evolutionary questions," he said.

Hopcroft and other polar researchers will now try to determine how long these species have been separated and whether they have drifted apart genetically.

David Barnes, of the British Antarctic Survey, said there a number of possibilities to explain how similar species live so far apart.

Some may have traveled along the deep-sea currents that link the poles or may have thrived during the height of the last ice age about 20,000 years ago when the polar environment was expanded and the two habitats were closer.

Hopcroft and Barnes cautioned that more work needs to be done to confirm whether the 235 species are indeed the same or differ genetically.

"Painstaking work by geneticists investigating both nuclear and mitochondrial genes will only be able to confirm this," Barnes said in an e-mail interview. "It may be they separated sometime ago but similar selective pressures have meant they have not changed much."