Floating through the eerie darkness, they look like special effects from a Hollywood space movie.
But these astonishing creatures, with their weird tentacles, translucent colours and smattering of spots and stripes, live far closer to home.
They are among the thousands of species discovered by marine biologists in an ambitious plan to record and name every living thing in the seas.
In the past year alone, the international team has identified 1,000 new plants and animals and shed light on the behaviour of hundreds of species.
The Census of Marine Life, a massive project involving more than 2,000 scientists from 82 nations, is now in its eighth year.
So far it has recorded 120,000 species but believes there could be as many as 250,000.
The finds include the deepest-living creature-ever discovered.
The 'comb jelly' lives 23,700ft below the surface in the Ryukyu Trench near Japan.
Other types of comb jelly were found under the Arctic pack ice.
Explorers found beds of giant oysters eight inches long in the Bay of Biscay and a giant mollusc more than 15 inches long off the coast of Louisiana.
The project has also thrown light on the origins of octopuses, proving that every deep sea octopus in the ocean evolved from one group living close to the South Pole millions of years ago.
Jesse Ausubel, Census of Marine Life programme manager at the Sloan Foundation in New York, said: 'Eight years ago a group of us set off to try to count all the fish in the sea.
'At the time people thought we were crazy, but eight years in we are fantastically excited and we are confident it can be done.
'We will have the first comprehensive census of marine life.'
Despite the efforts of the past few years, an estimated 95 per cent of the world's oceans remain unexplored.