There's more to jellyfish than stinging goo on the beach.
Starting Saturday, visitors to the National Aquarium in Baltimore will get a rare chance to see jellyfish as they really are -- delicate and mesmerizing creatures who are nettlesome to people only because they mistake swimmers for dinner.
"We want people to appreciate them as beautiful and interesting creatures, and not things to be afraid of," said Bruce Hecker, 43, the aquarium's curator of fishes and life support.
Called "Jellies: Phantoms of the Deep," the $500,000 exhibit has been leased for two years from the New England Aquarium in Boston. But the Baltimore aquarium has already begun breeding two of the eight species on display.
The exhibit will draw visitors into a darkened room where 11 dramatically illuminated tanks seem to pulsate and glow with these otherworldly creatures.
The sea nettles and moon jellies, lion's mane, umbrella, comb and "elegant" jellies range in size from contact lenses to tea saucers, and in color from white to pinkish-brown. Except for the bottom-dwelling "upside-down" jellies, they all drift gracefully in the lights in their specially designed tanks.
Their bodies, or "bells," trail long, thread-like tentacles and frilly ruffles in an eerie ballet with a New Age musical accompaniment. The displays reveal a delicacy and simplicity that is hard to see from a pier or boat. It vanishes completely when they wash onto a beach.
"They're very primitive very successful animals," Mr. Hecker said. Jellyfish are invertebrates. Scientists say they date back at least 650 million years, to a time long before the first animals with backbones evolved.
Despite the name, jellyfish are neither fish nor jelly. They are most closely related to sea anemones and corals. Their bodies are 95 percent water. What's left is nearly transparent, which helps them avoid being eaten.
They have muscles, light-sensitive "eyes," digestive systems and nerve cells, but no brains.
But they are probably best known for the nasty stinging cells in their tentacles. When the cells sense protein nearby, they fire microscopic harpoons.
The venomous barbs embed themselves in whatever they hit. Normally, it's the microscopic plankton, small fish and crustaceans that are food for the jellies. The harpoons remain linked to a jelly's tentacles by strong filaments. The prey is then drawn back into the frilly oral arms, which carry it into the bell to be digested.
"Man is an inadvertent victim; he's an accident," said Dr. Joseph W. Burnett, dermatology chairman and professor at the University of Maryland at Baltimore. He has been studying jellyfish and their effects on people for 29 years.
When a swimmer blunders into a jellyfish's tentacles, the stinging cells mistake human proteins for food. The venom can cause painful skin or eye injuries, as summer swimmers in the Chesapeake -- and the aquarium's employees -- have learned.
The rash and pain are not allergic reactions; they are the effects of an injected poison.
Stings by the Bay's Eastern sea nettles are not lethal. But a few species in tropical waters, where food is scarce, have evolved venoms powerful enough to guarantee that any encounter with a potential meal will be successful.
Dr. Burnett said at least two people are killed each year by such jellyfish, and dozens receive serious injuries.
The most lethal is the box jellyfish, which lives in waters between northwest Australia and the Philippines. It is not included in the aquarium show.
The pain of a box jelly sting is excruciating. "The scream is almost diagnostic," Dr. Burnett said. The caustic venom causes significant skin damage. But its poison also enters the blood stream and disturbs the vital transport of sodium and calcium across cell membranes.
"The first target organ is your heart, which is attacked within a half hour," Dr. Burnett said. "If you survive that, your respiration is affected in the next 4 to 5 hours. If you survive that, you face kidney death in 2 to 5 days, and liver death within a week."
Treatment includes supporting the victim's vital signs, administering an anti-venom, deactivating the tentacle fragments on the skin, and giving powerful pain killers. Dr. Burnett and his colleagues publish an international newsletter and operate a computer web site in an effort to educate doctors about the chemistry and toxicology of jellyfish stings.
Jellyfish with milder toxins gain advantage over their prey by extending their reach. The lion's mane jelly, which is included in the aquarium show, can grow tentacles as long as 200 feet -- longer than a blue whale.
Jellies can't pursue their prey. They only drift with the current. The rhythmic contractions of their bells looks like swimming, Mr. Hecker said, but is mostly a pumping action that draws food within reach.
As threatening as they are to swimmers, the jellies' weapons don't protect them from predators. They are eagerly eaten by sea turtles and whales. But these predators often get sick or die from eating floating plastic refuse that they mistake for jellyfish.
People in some Asian countries consider dried jellyfish a delicacy. "They taste just how you figure they'd taste: fishy and oceanic," Dr. Burnett said. He likened the texture to "a soggy cracker."
Aquarium display of jellyfish is a science pioneered only recently by the Monterey Bay Aquarium. While they resist infection, jellyfish are vulnerable to injury. They require special tanks with constant currents, and no corners or pump intakes where jellies might get trapped. Aeration systems must protect jellyfish from bubbles, which can be lethal.
The central filters must screen out tentacle fragments. Jellyfish with weaker venom are vulnerable to those with stronger venom, and contact with stinging cells from a stronger species could kill them.
Aquarists at the New England Aquarium in Boston learned the art in Monterey, and built their own jellyfish exhibit, which was extremely popular during its yearlong run.
Baltimore aquarists have redesigned and expanded the exhibit and have begun a breeding program. They also are breeding the brine shrimp and young jellies that the display's inhabitants will eat.