ONTEREY, Calif. -- For every extraterrestrial creature we haven't discovered on Mars or in a galactic suburb, we have invented one to satisfy our outer-space imaginings.

But for every E.T., there is a real, earthbound creature as strange, as otherworldly, as cute.

Consider the predatory tunicate, an amusing, 6-inch-tall, see-through critter living 5,000 feet under the sea, rooted to the steep walls of the submarine Monterey Canyon by its cylindrical stalk. Atop that stalk, the tunicate wields a gaping Muppet-like mouth (oral hood) for trapping prey.

The tunicate, inhabiting a low-oxygen environment as alien to humans as the Martian atmosphere, is an overnight celebrity of "Mysteries of the Deep," a one-of-a-kind exhibit at the Monterey Bay Aquarium in Northern California. The exhibit features 46 strange-but-true species collected from so deep it took a two-ton robot to get them.

The creatures are from the floor, walls and midwater of the bay's canyon. Their realm is off-limits to pedestrians, whose heads would shrink to key-chain souvenir size under pressure of nearly three tons per square inch. Sunlight cannot reach there.

After a decade of effort and a $5 million expenditure, research biologists and aquarists at the aquarium and the Monterey Bay Aquarium Research Institute, have learned how to keep these bizarre and rare animals alive outside the canyon. The result has astonished even seasoned marine biologists who never thought they'd have access to a live, not pickled, tunicate.

Michael Hutchin, director of conservation and science for the American Zoo and Aquarium Association in Silver Spring, believes the exhibit is proof that "Star War creatures already exist."

Though a science fiction buff, Hutchin says that what is "truly astonishing is that those things do exist. They may be very small ... but there are incredible things that exist out there in nature, that go beyond your wildest imagination."

Scientists estimate that 10 million species inhabit the deep ocean, compared to 1.4 million described so far on land.

"From a research point of view, it's an incredibly important development," Hutchin says. "It's a window on another world and the education potential of the exhibit is also tremendous."

Viewing the exhibit is like strolling through a make-believe garden where mushroom soft coral blooms, pom-pom anemones slowly curl and uncurl their tentacles to nab krill, a bioluminescent comb jelly blinks like a Broadway marquee, and a deep sea-floor octopus seems to peer at you with unsettling humanoid eyes. An eerie soundtrack underscores the realization that the ocean's depths yield life as weird as anything not yet found in the heavens. It is a dark underworld undulating and pulsing with strange beauty.

Visitors meet such whimsical creatures as the peppermint gorgonian and the red licorice gorgonian. Brightly colored corals, they are flexible enough to survive strong currents and range in depth from 130 feet to 5,500 feet.

The gorgeous mushroom soft coral resembles an exotic bouquet. Found in depths up to 4,000 feet, it uses its lily-look-alike tentacles to snare drifting food.

The pallid eelpout inhabits the midwater, where there are no hard surfaces to rest on. They curl into hoops when disturbed and the black lining inside their stomach obscures the bioluminescent light of their prey.

Also living in midwater, the giant red mysid's intense color is its camouflage in deep waters where the color red vanishes. This shrimp-like animal releases a cloud of bioluminescent fluid when disturbed.

On seafloor as deep as 3,300 feet, the lovable spotted ratfish munches on brittlestars, worms and other low-lying animals. Related to sharks, ratfish have rabbit-like faces, smooth skin and large green eyes.

The extreme conditions that sustain such biological curios have made them extremely difficult to observe in their natural habitat, much less capture and keep alive: the pressure, a temperature hovering around 39 degrees, low oxygen requirements and quirky feeding habits.

Gilbert Van Dykhuizen, an aquarist who has worked since 1989 on "Mysteries of the Deep," displays an obvious affection for the critters he has brought to the surface of the ocean and public consciousness. Tall, craggy and sea-weathered, Van Dykhuizen stands in his office tucked away in the sprawling aquarium's deep-sea lab, where understudy tunicates, Sea whips and other animals await their star turn.

He recalls when marine biologists gathered at the research institute from around the world to brainstorm about developing techniques for retrieving deep-sea creatures. They were "skeptical it was going to happen," he says.

Trial and error led Van Dykhuizen and his colleagues to success on a relatively moderate budget. Deep-sea exploration "is not an area funded heavily at all," the scientist explains. Rather than attempt costly and over-ambitious goals, "We wanted to keep it simple," he says. Weeding through a wish list of 150 species, the aquarists decided to search for animals that could be acquired on a regular basis, exhibited well and would be appealing to visitors.

Research institute and aquarium staff retrieved the animals using the submersible, a Volkswagen Beetle-sized robot, equipped with video camera, collecting gear, flood lights and sonar. Working from a high-tech research vessel on the surface, pilots in the control room monitored what the robot, as much as 3,300 feet below, saw on a color television screen. By remote control, they manipulated the robot's electronic arm to capture animals they sought.

They are "masters of what they do," Van Dykhuizen says. Even for the masters, it was an arduous and often frustrating experience. Rough waters, seasickness and locating sites where animals subsisted in ample supplies proved challenging enough. The crew also had to learn how to capture the fragile creatures gingerly, as even a slightly less-than-gentle encounter with the robotic claw arm could prove fatal.

Sometimes the solution was as simple as attaching two kitchen sponges to the robot's arm. Then, when the pilots found a group of long, skinny sea-whips, the sponge-enforced arm "plucked them like carrots out of the sediment," Van Dykhuizen says.

To round up pom-pom anemones, which rolled defiantly away from the robot, aquarists attached a kitchen colander and scooped.

The pilots also learned not just to take a tunicate or mushroom soft coral, but the rock that held it, so as not to crush the creatures.

The aquarists ruled out trying to capture some of the denizens of the canyon's midwater. Comb jellies, larvaceans and others were too gelatinous or otherwise too delicate to support at sea level. The deep-sea siphonophore, a broom-stick-thin meandering colony of stomachs and stinging tentacles, was plainly impractical. (Many of the unretrievable are seen on a tape at the exhibit.)

Poorly ossified skeletons eliminated dragonfish, hatchetfish, viperfish and other midwater fish because they soon disintegrated after capture. In general, researchers determined that reproducing the highly pressurized conditions for animals who required it was too complex and would be a poor visual payoff for visitors.

The aquarists' other major challenge was keeping animals in captivity alive for prolonged periods. "Patience is key and being very observant about how the animal is doing," Van Dykhuizen says. Often he and colleagues "had to backtrack and play Sherlock Holmes -- what should I change? [What do we] need to tweak here and there? [Should we] adjust the temperature, the lighting and other environmental factors?"

All the while, aquarists made significant discoveries. Van Dykhuizen says he was "blown away" by all the new information.

Puzzled over the tunicate's six-month life span in captivity, he realized its oxygen demands were much lower than anticipated. Too much oxygen causes tissue and cell damage. Now that the oxygen concentration has been ratcheted down to deep-water levels, which can be as low as one-hundredth the amount found in surface waters, tunicates are surviving up to two years in captivity, and it is hoped they will begin to reproduce.

The aquarists also figured out how to keep alive the shortspine thornyhead, a fish that can live as long as a century in cold, deep water. By intercepting juvenile rockfish before their drop to deeper water, they prevented the species from producing the enzyme vital for survival in highly pressurized waters.

The creatures, for whom a meal consists of "marine snow," the steady fall of dead plankton and animal wastes from the ocean's upper-reaches, had to be fed. Aquarists fix them "krill shakes," a blend of krill and sea water that replicates snow, and is delivered via turkey baster.

In its media promotions for "Mysteries," the Monterey Bay Aquarium announces more people have walked on the moon than on the deepest ocean floor. The message is a way of driving home a point: The oceanic frontier is just as mysterious, just as difficult to probe, and perhaps more relevant to our lives than the moon.

"Is the predatory tunicate vital to national security? Probably not," Van Dykhuizen says. Yet, there is a push among conservationists and scientists to increase awareness of the ocean's environmental significance and resources for its exploration. In a Newsweek essay, Russell A. Mittermeier, president of Conservation International, a Washington nonprofit organization dedicated to preserving biodiversity, wrote of this desired sea change: "The justification for spending millions of dollars to send probes to these planets is much the same as that used by field biologists surveying the flora and fauna in poorly documented ecosystems on Earth. ... But we languish in the Dark Ages when it comes to understanding the diversity of life on Earth."

This "is our planet, we live on it," Hutchin says, making the same point. "It's the only thing we have and we're destroying it at a very rapid rate. It behooves us to focus on the conservation of biodiversity of the planet."

The thought is put in more elemental terms by a young visitor who wrote: "I would love to explore the canyon walls and really touch a tunicate."

"Mysteries of the Deep," continues through Jan. 6, 2002. Monterey Bay Aquarium: (831) 648-4918.

Pub Date: 4/10/99