Revealed: Meet the creatures of the deep who have never before been seen before

An undersea "census" has discovered a menagerie of new marine creatures, but has also mapped a "dead zone" where the Boxing Day tsunami killed everything in its path.

The Census of Marine Life, a global partnership of 1,700 scientists from 73 countries, contains more than 40,000 of an estimated 230,000 marine species described by science - perhaps only a tenth of the actual number of animals living in the sea. Of these 40,000 known species, 78 are marine fish that were added this year. The total number of marine fish species now included in the census database comes to 15,717.

New creatures discovered include an unusual species of jellyfish-like organism called a siphonophore - which grows as colonies of individuals attached by a central thread, and the strange bottom-dwelling Aphyonus gelatinosus, a fish that is covered in a gelatinous layer, found in the northern part of the undersea ridge running down the middle of the Atlantic Ocean.

Victor Gallardo, a marine biologist from Chile who sits on the Census steering committee, said that the immense scale of the deep-sea environment meant that much of its life was a complete mystery. "The deep-sea floor is an area of 300 million square kilometres, of which the area sampled to date is equal to a few football pitches," Dr Gallardo said.

There are between 30,000 and 100,000 subsea mountains - where some of the most unusual species live - yet only about 50 of them have been surveyed.

Experts who sent robot submersibles to the epicentre of the quake, some 2.5 miles below the Indian Ocean, also found a barren strip of the sea floor several miles long, where the tsunami that wreaked such havoc in land had a correspondingly apocalyptic effect underwater.

They said that the total absence of life was "unprecedented" in 25 years of deep-sea sampling and could be the result of a massive underwater land slip.

Professor Ron O'Dor of Dalhousie University in Nova Scotia said that in general the deep-sea surveys found little or no effect of the Boxing Day tsunami-earthquake except for this one site off the Indonesian island of Sumatra. "This is along the earthquake's fault line and what probably happened was that some underwater cliff collapsed and there was a big landslide," he said. "As far as I know, no one has been on a zone like this so quickly after an underwater earthquake. The sea is rich in life, and you'd expect a site like this to be quickly recolonised, but that hasn't happened. It's unprecedented.

"Normally when you go to the bottom of the sea anywhere and take a sample or look around, there's always something alive. But five months after the earthquake this entire plain created by the collapse of this cliff was essentially devoid of life."

The dead zone measures about 200 metres across and extends for at least several kilometres, although the scientists only managed to survey a small section of the fault line in an 11-hour dive.

"At this depth the temperature does not rise above 4C which is cold enough to make sure that any regeneration of life takes place only slowly," Professor O'Dor said. "It would be wrong to portray this is a natural disaster on the scale of the effects of the tsunami on the coastline because this sort of underwater event probably occurs quite frequently."