Jellyfish

雪儿 · 发表于: 2011-7-8 10:48:21

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Mosaic Jellyfish

Photograph by Melissa Fiene, My Shot

A mosaic jellyfish floats serenely in the waters of the Coral Sea, about 100 nautical miles from Cairns, Australia. Jellyfish are ubiquitous in the Earth’s oceans. They can thrive in warm water and cold, along coastlines or out in the deep. Their bodies are about 95 percent water. And though they have no brains, jellyfish have somehow been smart enough to survive for over 500 million years.

雪儿 · 发表于: 2011-7-8 10:48:33

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Moon Jellyfish

Photograph by David Doubilet, National Geographic

These translucent jellyfish are named for their resemblance to Earth’s satellite—but the species has had an otherworldly experience. In 1991 moon jellies flew aboard the space shuttle Columbia during a study on weightlessness and the development of juvenile jellyfish. Here on Earth, the jellies are commonly found in warm ocean waters worldwide.

雪儿 · 发表于: 2011-7-8 10:48:46

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Purple-Striped Jellyfish

Photograph by David Doubilet, National Geographic

A large, purple-striped jellyfish floats in the waters of California’s Monterey Bay, where they sometimes arrive en masse. This jelly can grow up to three feet (one meter) in diameter and appear rather formidable. But its stinging tentacles are used to bring in mostly smaller prey, including zooplankton, larval fish, and fish eggs.

雪儿 · 发表于: 2011-7-8 10:48:57

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Jellyfish in Lagoon

Photograph by David Doubilet, National Geographic

With a distinctive pulsing motion, a jellyfish makes its way through the waters of a Pacific lagoon. Most jellyfish tend to simply drift along with prevailing currents. But some use more active methods of self-propulsion, including shooting a stream of water from their mouths. A jellyfish also uses its large, central mouth to consume food and expel waste.

雪儿 · 发表于: 2011-7-8 10:49:08

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Pacific Coast Jellyfish

Photograph by Paola Carolina Smania, My Shot

Jellyfish use their dangling tentacles, equipped with hollow, harpoonlike darts loaded with neurotoxins, to sting fish, shrimp, or crabs. The strike leaves its victim stunned for easier consumption. Humans can also receive a painful sting from these toxic tentacles, even those belonging to beached or dead jellyfish. In the case of a few species, like Australia’s notorious box jellyfish, stings can be fatal.

雪儿 · 发表于: 2011-7-8 10:49:20

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Lion’s Mane Jellyfish

Photograph by Paul Nicklen, National Geographic

A curious yet cautious diver approaches a lion’s mane jellyfish off the British Columbia coast. The tentacles that make up this jelly’s “mane” can deliver a painful and even potentially fatal sting. But such toxins don’t deter several fish species from feeding on the ample bulk of the cold water-loving jellyfish.

雪儿 · 发表于: 2011-7-8 10:49:30

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Comb Jelly

Photograph by Jason Edwards, National Geographic

Ctenophores are commonly called comb jellies because they use rows of hairlike cilia to propel themselves through the water. This unique physiology also causes comb jellies to refract light, so they often shine with a rainbow of iridescent color. In the absence of sunlight, comb jellies can still be colorful, if less vivid. Most species are bioluminescent.

雪儿 · 发表于: 2011-7-8 10:49:41

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Mastigias Jellyfish

Photograph by Tim Laman, National Geographic

Does this humble jellyfish help determine Earth’s climate? Studies of these Mastigias jellies in a landlocked Palau lake recently prompted scientists to suggest that the motion of sea animals plays a major role in seawater mixing. Winds and tides are major ocean mixers but sea creatures—including jellyfish—may account for as much as a third of the total, the study suggests. That would mean jellies are significant drivers of ocean circulation patterns and thus help to determine Earth’s climate.

雪儿 · 发表于: 2011-7-8 10:49:53

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Crab Carrying Jellyfish

Photograph by Tim Laman, National Geographic

Cassiopea andromeda, the upside-down jellyfish, is named for one of Greek mythology’s treacherous queens. Cassiopeia was punished by Poseidon, who deemed that her constellation often appear upside-down in the sky. Her namesake jelly often lies on the seafloor with its mouth and arms facing the surface, which allows symbiotic algae to collect sunlight for photosynthesis and pass nutrients along to the jelly. Crabs sometimes carry these jellyfish on their backs to serve as a very effective protective shield.

雪儿 · 发表于: 2011-7-8 10:50:20

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Crab on Purple Jellyfish

Photograph by David Doubilet, National Geographic

Some animals, like these young crabs and some juvenile fish, can live unharmed among a jellyfish’s venomous tentacles. There, protected from prey, they feed on jellyfish leftovers like zooplankton or larval fish and remove parasites from their accommodating hosts.

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