It's Alive Animals

Hunchbacked conchs jump at the smell of danger

WHEN CONCHS GET SCARED Among jumping snails, hunchbacked conchs are some of the most vigorous.

S. Lefevre/Univ. of Oslo

By Susan Milius

November 3, 2015 at 11:00 am

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A whiff of danger makes hunchbacked conchs so jumpy they actually jump.

“A very peculiar movement for a snail,” says Sjannie Lefevre of the University of Oslo in Norway.

Admittedly, the motion of Gibberulus gibberulus gibbosus is less boing-boing and more kerflop-kerflop. But each push-off can send the small, striped conchs in Australia’s Great Barrier Reef several centimeters above the sea bottom and almost a body length (3 or 4 centimeters) forward. They can keep at it too, jumping as many as 100 times in three to five minutes.

The sea snails save their jumping for conch emergencies, such as when they detect dissolved body odor from the deadly cone snail Conus marmoreus. Cone snails glide rather than jump. But if a cone snail gets close enough, it harpoons the conch with a long, venom-delivering proboscis that is as agile as an elephant’s trunk. Then it reels in the paralyzed conch like a fish on the line.

Such threats favor epic jumping in spite of the conch circulatory system, which looks inefficient at first glance. Unlike vertebrates, which sluice their blood through vessels in a closed, recirculating system, conchs and other snails pump blood away from the heart in arteries that just — end. Blood floods outward, spreading and washing over organs to deliver oxygen and nutrients. The blood then seeps back into veins that channel it eventually to the heart for another spurt.

When a conch jumps, this spurt-and-leak circulation supplies tissues with four to six times the oxygen delivered when the snail just chills, Lefevre and colleagues report in the Oct. 1 Journal of Experimental Biology.

In one measure of athletics, the kerflopping conch outperformed some agile, darting reef fishes. As researchers pushed water temperatures to 38° Celsius, the conch kept jumping. And its circulatory system still comfortably delivered ample oxygen. This kind of heat is less comfortable for many reef fishes, Lefevre says. “They’d be dead.”