Mystery Of The Pistol Shrimp's Underwater Cannon Solved

A snapping shrimp with its powerful claw. Matthew R McClure/Shutterstock

Scientists have worked out how alpheidae, also known as pistol shrimp, are able to close their claws so quickly that they can create shockwaves that stun their prey.

Pistol shrimp may only measure around 3-5.5 centimeters (1.2-2.1 inches) long but their claws pack a powerful punch. Able to fire jets of water at speeds of 30 meters (100 feet) per second that can immobilize prey, they produce sound at 200 decibels, which is louder than a .22 caliber rifle shot.

Now, in a paper in Current Biology, researchers have explained how this happens. The claws have a unique slip joint, which is able to close incredibly rapidly, producing the powerful effect.

The claws close so fast that they can boil the water around them, producing tiny air bubbles. As the water pressure crushes the bubbles, it produces a shockwave.

Looking at the claws of 114 shrimp species, the researchers found two types of unique joints – a slip joint similar to that seen in a Swiss Army knife, with a tiny ridge that creates pressure when the claw closes, letting it snap shut quickly.

A cocking slip joint seen in some shrimp allows the claw to build up muscle tension. Using 3D-printed models of joints, they found that a claw with this joint can snap shut with enough power to produce a shockwave.

“How energy is stored during cocking remains unclear,” the researchers note in their paper, suggesting that elastic elements in the muscle may play a part.

Research last year showed us that the claws produced air bubbles thanks to the friction between the jet it produced and the water surrounding it. This created a vortex with a void in the center that, when it collapsed, produced a powerful pressure wave – all in less than half a millisecond.

Now thanks to this latest paper, we’re closer to understanding how the claw itself works. This looks to be an incredible evolutionary trait, one that has given this rather small creature a powerful advantage on the ocean floor.

“Remarkably, these key functional transitions between ancestral (simple pinching) and derived (snapping) claws were achieved by minute differences in joint structure,” the team writes.

(H/T: Science)

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