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 / Updated  / Source: Live Science
By Tia Ghose, LiveScience

The sunlit upper layer of the world's oceans is teeming with tiny creatures that seem to have jumped off the pages of a Dr. Seuss tale, with exquisite see-through bodies, bulging eyes and an array of glowing colors. These mysterious sea characters may form the bulk of ocean life, new data from a three-year voyage suggests.

Many of the newly discovered organisms are single-celled and bigger than bacteria and viruses, but smaller than visible sea life, according to several studies published this week in the journal Science.

"The ocean has always been this big, unexplored world full of mysterious and usually big things, but a century and a half of oceangoing ships around have found all the big things," said Stephen Palumbi, a marine biologist at Stanford University's Hopkins Marine Station in Pacific Grove, California, who wrote a Perspectives piece about the expedition in the same issue of Science.

This small medusa collected in the Mediterranean Sea is a close relative of Turritopsis, thought to be an immortal jellyfish.Christian Sardet / CNRS / Tara Expeditions

Now researchers have cataloged many of the mysterious life-forms that "are 2 millimeters [0.08 inches] across all the way down to the parasites and viruses and the zombie vampire bacteria that feed off of them." [See Images from the Epic Sea Voyage and Wacky Creatures]

The new work was part of an epic, three-year voyage taken by more than 150 scientists on a 36-foot (11 meters) schooner called the Tara. The team visited 210 stations throughout the world's oceans, navigating around pirates in the Gulf of Aden and braving icy storms in the Antarctic, said Chris Bowler, a plant biologist at the Ecole Normale Supérieure, Institut de Biologie de l'ENS in France.

Because these creatures are invisible to the naked eye, the team teased them out by looking for their genetic material in thousands of water samples collected at those hundreds of stations.

"We sampled an entire microscopic ecosystem covering viruses, bacteria, protists and small organisms," Bowler said. Those creatures covered a range of sizes equivalent in scale to "going from an ant to a Brontosaurus," he said.

Some of the collected DNA matched that of known species, but other genetic material pointed to thousands of completely unknown organisms. Most of these mysterious sea creatures were single-celled or simple multicellular eukaryotes, meaning they were organisms with a cell nucleus and other membrane-bound internal structures. Many of them were predators that specialized in engulfing other single-celled organisms.

Surprisingly, this mysterious trove of tiny eukaryotes is incredibly interactive, with parasites, predators and symbiotic creatures that rely entirely on each other for mutual survival all rubbing up against one another in a crazy carnival of species, Palumbi said.

"They're forming these complex but very tiny ecosystems that are probably holding the entire web of life in the ocean together," Palumbi told LiveScience.

This is a condensed version of a report from LiveScience. Read the full report. Follow Tia Ghose on Twitter and Google+. Follow LiveScience on @Twitter, Facebook and Google+.