<p><strong>A female violet snail, <em>Janthina exigua</em>, hangs from a float of homemade mucus.</strong></p><p>Scientists have long observed snails "surfing" the oceans on such rafts, which can serve as flotation devices, egg-storage areas, and platforms for young snails.</p><p>But it was unknown how the family of fewer than ten bubble-rafting species evolved their odd lifestyles, said <a href="http://www.lsa.umich.edu/eeb/directory/graduates/celiakc/default.asp">Celia Churchill</a>, a Ph.D. student at the University of Michigan in Ann Arbor.</p><p>Churchill had already suspected that bubble rafters evolved from bottom-dwelling snails that produce mucus-filled egg masses. To pinpoint the rafting snails' closest relatives, the team sequenced DNA from bubble-rafting species and other potential "sister families," using molecular techniques to piece together an ancestral family tree.</p><p>The results revealed that bubble rafters descended from a bottom-dwelling snail called the wentletrap, which still exists today.</p><p>Both snail groups secrete mucus from their feet-muscular organs at the bases of their bodies. But instead of making egg masses, the bubble rafters use the quick-hardening mucus to create rafts with the "consistency of bubble wrap," said Churchill, whose new study appeared recently in the journal <em><a href="http://www.cell.com/current-biology/">Current Biology</a></em>.</p><p>"You can pop it if you get a fresh one."</p><p>(See <a href="http://news.nationalgeographic.com/news/2008/10/081020-snails-walking-water.html">"How Snails Walk on Water Is a Small Miracle."</a>)</p><p><em>—Christine Dell'Amore</em></p>

Snail Surfer

A female violet snail, Janthina exigua, hangs from a float of homemade mucus.

Scientists have long observed snails "surfing" the oceans on such rafts, which can serve as flotation devices, egg-storage areas, and platforms for young snails.

But it was unknown how the family of fewer than ten bubble-rafting species evolved their odd lifestyles, said Celia Churchill, a Ph.D. student at the University of Michigan in Ann Arbor.

Churchill had already suspected that bubble rafters evolved from bottom-dwelling snails that produce mucus-filled egg masses. To pinpoint the rafting snails' closest relatives, the team sequenced DNA from bubble-rafting species and other potential "sister families," using molecular techniques to piece together an ancestral family tree.

The results revealed that bubble rafters descended from a bottom-dwelling snail called the wentletrap, which still exists today.

Both snail groups secrete mucus from their feet-muscular organs at the bases of their bodies. But instead of making egg masses, the bubble rafters use the quick-hardening mucus to create rafts with the "consistency of bubble wrap," said Churchill, whose new study appeared recently in the journal Current Biology.

"You can pop it if you get a fresh one."

(See "How Snails Walk on Water Is a Small Miracle.")

—Christine Dell'Amore

Photograph courtesy Denis Riek

Pictures: How Bubble-Rafting Snails Evolved

Scientists have cracked an evolutionary mystery: How did some snails come to "surf" the oceans on mucus-bubble rafts?

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