How This Tiny Sea Criter Hits Like Mike Tyson

At less than A quarter of an inch long, the amphipod – a crustacean that looks a bit like a shrimp – leads a relaxed life, sifting through algae along the east coast. Well it is shallow relaxing, as scientists have just discovered. A male amphibian swings a huge claw that can exceed a third of its mass, and when it snaps into place in less than a 10,000th of a second, it sends a supercharged jet of water to signal its displeasure. Thanks to a $ 150,000 camera shooting at 300,000 frames per second, researchers have captured a male amphipod in the act for the first time, a moment so violent it’s almost enough to detonate the animal.

You are probably wondering how to piss off a male amphibian experimentally – more specifically the species Dulichiella cf. appendiculata. So I’ll tell you. While working in the lab, the researchers glued toothpicks to the animals’ backs and attached the toothpicks to ‘micromanipulators’, which allowed them to accurately position the amphipods. All they had to do was dangle some of the hairs from a brush near the amphipods, violating their personal space. And then, SNAP. “So obviously they’re using it in an aggressive context,” said Sheila Patek, Duke University biologist, co-author of the paper.

While the high-speed camera was rolling, Patek and her colleagues suddenly made the invisible visible. “It’s almost magical in a way,” says Patek. In the past, you might only hear or feel an amphipod pop when you had one in a container, not when you looked at it in the wild. “But to get the whole thing in focus and beautifully lit, you suddenly see this little appendage filling the screen, loading, and then clicking,” she says.

The crucial part of that appendix, more formally known as a gnathopod, is called the dactyl. In the image above, that’s the long, leaf-like structure at the top of the claw. It is no thicker than human hair. To break, the amphipod contracts a muscle, pulls that dactyl back, and stores an incredible amount of energy. Patek and her colleagues need to do more work to fully understand the morphology of how the click works, but a latch is likely to hold the dactyl in place. When the animal is ready to break, it releases the latch, suddenly releasing the stored energy of the claw.

‘And when we looked even further, we said,’ Wait, there’s one water jet get out of there! ‘”Says Patek. More specifically, the force of the claw cut seems to push the water at an oblique angle rather than perfectly straight ahead. And then, oh my god, every now and then the jet of water seems to cause cavitation, that is the formation of these vapor bubbles, which happens when you flow at these extraordinary velocities. “When these little cavitation bubbles collapse, they go explode, unleash an explosion of energy. In fact, this kind of force is so powerful that when boat propellers create their own cavitation bubbles, the force chews away on the metal of the blade over time.