Snails With Boots of "Fool’s Gold"

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Researchers have discovered a new type of snail living on the seafloor that makes quite a quirky fashion statement. It wears an armor of shiny scales over the soft part of its body that pokes out from its shell. This part of the snail is called its foot…. Maybe scientists should call this unusual covering its “boot?”

The scales are made of two iron-rich minerals. One is greigite and the other is pyrite, which many rock collectors often call “fool’s gold” because of its golden color. The scientists who discovered the snail still aren’t sure what the purpose of the scaly armor purpose is. It might help protect the snail against predators.

The snail lives at the base of columns called “black-smoker chimneys” on the floor of the Indian Ocean. Columns of hot water spout through the chimneys, carrying minerals that give the water a black color. Just like the Old Faithful geyser at Yellowstone National Park, this erupting water was heated by volcanic rock below the Earth’s crust. The minerals in this seafloor geyser are rich in iron and sulfide—the same ingredients that the snail’s armored boot is made of.

Although they’ve never seen any other animals use iron sulfides in this way, Anders Warén of the Swedish Museum of Natural History in Stockholm, Sweden and his colleagues think that this snail somehow sucks the minerals out of the water and uses them for growing its scales.

By studying the snail’s DNA and its anatomy, Warén and his colleagues learned that the snail evolved relatively recently (that is, recently in evolutionary time) and probably couldn’t have evolved without the black-smoker chimneys nearby. The researcher’s study appears in the 7 November issue of the journal Scence, published by AAAS, the non-profit science society.

—Kathy Wren

6 November 2003