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Armor-Plated Snail Discovered in Deep Sea

John Pickrell
for National Geographic News
November 7, 2003
 
Researchers have found perhaps the world's most unusual snail. The
as-yet-unnamed creature bears a mass of interlocking, iron-based plates
on its body and the base of its foot. Like a suit of medieval armor, the
snail may use its metal scales as a defense against predatory attack.

As gardeners already know, all other slugs and snails (or gastropod mollusks, to the experts) sport a soft and slimy foot.

The new snail, described in the current edition of the journal Science, was discovered in the hostile hydrothermal vent environment of the deep Indian Ocean.


"Strange Little Beast"

Anders Waren, a biologist at the Swedish Museum of Natural History in Stockholm and the lead researcher behind the find, said this "very strange little beast" is the first animal discovered that uses iron sulfides for a structural purpose.

Waren said that when he first examined the sea snail, the animal's magnetized scales kept sticking to his forceps. He guessed that an iron mineral was involved.

While unique to modern animals today, the snail's scales bear a remarkable resemblance to scales found on many of the earliest complex animals, particularly those from the Cambrian Period 540 to 500 million years ago. Genetic and anatomical tests, however, reveal that the new species is related to other common groups of modern snails.

The snail's scales are comprised of two iron sulfide minerals: pyrite, more commonly known as fools gold, and greigite. Waren said that the general instability of sulfides explains their rarity as a biological building material. However, he noted: "That may not be the case at such depths." Iron and sulfur compounds are abundant in the mineral-rich waters of hydrothermal vent ecosystems.

Cindy Van Dover, a marine biologist at the College of William and Mary in Williamsburg, Virginia, and study co-author, was on the team that found the snail during an expedition to Indian Ocean's Kairei hydrothermal vent field in 2001.

Expedition researchers used a remotely operated submarine to explore the 1.6-mile-deep (2.5-kilometer-deep), black vent environment and collect samples for analysis. The researchers found many species new to science, but "this is certainly the strangest so far," said Waren.

Black Smokers

The armor-plated species was found at the base of geyser-like underwater mineral chimneys known as black smokers. The structures explosively belch forth super-heated, 750° Fahrenheit (400° Celsius) black water previously trapped in molten rock below the Earth's surface. The water is prevented from boiling due to the enormous pressure (250 times greater than that on land) found at those depths. Cooler water near the chimneys carries many of the minerals that account for the flows' black color, including the constituents of those minerals found in the snails' armor plating.

"Hydrothermal vents support a unique…fauna that's giving us exciting insights into evolution, adaptation, and the early history of life on Earth," said Callum Roberts, a mollusk expert at the University of York, England. "These vents represent an outstandingly rich natural ecosystem that we should cherish and protect as vigorously as any of our national parks on land," he added.

Mary Seddon, a World Conservation Union (IUCN) mollusk specialist and biodiversity scientist at the National Museums and Galleries of Wales in Cardiff, said: "It's only been with the [recent] advent of remotely operated vehicles that we've been able to sample these [secluded] habitats." Such habitats are turning up some highly unusual creatures exquisitely adapted to living in harsh conditions, she said.

The researchers suspect that the snail's armor plating could be a defense against other predatory snails that co-exist in the vent community. Warren, the study leader, said the scales look like they would effectively block the specialized teeth predator snails use to inject venom.

As Roberts noted: "This is yet another extraordinary beast from a remarkable habitat."
 

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