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A previously unidentified species of whale has been recorded by researchers.

The creature is a close cousin of the blue whale and has been given the formal scientific name Balaenoptera omurai, reports the journal Nature.

Its Japanese discoverers say the 12-metre-long animal's DNA and anatomical features mark it apart from other whales that use combs to trap food.

Commentators believe the new finding may complicate the debate over whether commercial whaling should be resumed.

It was likely to delay any return to the regular harpooning of certain whale species, they told the BBC.

Food trap

The new discovery was made by a team led by Shiro Wada of the National Research Institute of Fisheries Science in Yokohama.

They examined the DNA of a number of individual whales belonging to the species known as Bryde's whale, also called Eden's whale.

There has been debate for many years over whether this species has the correct taxonomic classification.

"The classification of these whales has been confusing because Bryde's whale has often been confused with Eden's, and we didn't know whether it's one species or two," Dr Wada told the BBC.

His team now argues that in fact there are three separate species - Bryde's, Eden's - and a new whale species, omurai.

All are so-called baleen whales, which use a comb, or baleen plates, to trap their food, such as krill. They belong to the rorqual sub-group which have throat grooves that expand as they feed.

Controversial 'science'

If the team's assessment is accepted by the international scientific community, it will at a stroke increase the number of known living rorqual species from seven to nine.

The others are the blue whale, which is the world's largest mammal; fin, sei, common and Antarctic minke, and the humpback whale.

The new findings are based on the study of a dead whale that was washed on to the shore of the Japanese island Tsunoshima in 1998, and several other specimens caught 30 years ago by the often-criticised Japanese scientific whaling programme.

"Without that programme, we would not have made this discovery," Dr Wada stressed.

He said the separate species classification for B. omurai was attributed to its distinct DNA profile, its cranial structure and, in particular, the mammal's smaller number of baleen plates.

Big finding

Commenting on the discovery, Professor Bo Fernholm, from the Swedish Museum of Natural History in Stockholm, and a former chair of the International Whaling Commission, said the evidence was "quite convincing".

He also said the research could impact the debate over whether countries such as Japan, Norway and Iceland were allowed to resume commercial hunting of whales.

"This is important because the Japanese want to hunt Bryde's whales.

"The situation then becomes more complex if Bryde's whale is in fact three species."

Estimates of the number of the Earth's species yet to be discovered vary wildly but all are high - some more than 100 million.

These are thought to be mainly fish, fungi, microbes and insects - on the whole very small organisms.

The identification of a new mammal species is a rarity, especially one as big as a whale.