Only the diameter of a belly button, this amphipod is the fastest creature in the ocean

A new study from the University of Alberta found an unusual amphipod that can accelerate as fast as a bullet.  

Amphipods are sediment-burrowing crustaceans, found in fresh and salt waters around the globe, known locally as beach-hoppers or scuds. There are almost 10,000 known amphipods in the world. 

Dulichiella appendiculata is found in the Atlantic ocean, off the east coast of the United States. Males snap their large claws — which are roughly a quarter of their body mass — to make the ultra-fast movements from a standstill to over 100 km/h within milliseconds. 

“What’s amazing is that an animal this small can move that fast,” Richard Palmer, retired marine biologist at the University of Alberta who led the study, said while on CBC’s Radio Active last Monday.

Other species can move faster, such as jellyfish that shoot out stinging nettles. But those stinging nettles are a one-off, whereas these amphipods are the only known creatures in water that can repeat the same fast movements, Palmer said.

Despite it’s high acceleration, the amphipod only moves millimetres.

The amphipod Dulichiella appendiculata, shown here next to a coin, is about one centimeter in length. (Suppled by Richard Palmer )

Its snapping claws are so fast and sudden, however, that they rip water molecules apart and create underwater explosions called cavitation bubbles, said Palmer.

To clock the amphipod’s movements, Palmer’s team used cameras that are normally used in high-speed automobile accidents that take pictures at nearly 500,000 frames per second.

This new find could be particularly important for future technologies. Learning about how the amphipod moves could help engineers develop new small robotic structures that move extremely fast, said Palmer.

In the meantime, however, scientists are left wondering why the amphipod has to move so fast, said Palmer.

“I wish we knew,” he said. 

Charles Darwin’s theory of evolution suggests the species would have eventually developed such speed out of necessity.

WATCH | Unusual amphipod has excellent acceleration:

Dulichiella appendiculata are the only known creatures in water able to repeat the same fast movements over and over again, according to Richard Palmer, a retired marine biologist at the University of Alberta. 0:12

Only males have the claw, so it’s most likely related to sex — such as fighting with other males, defending females from males, or possibly trying to attract other females to mate, he said.

“But we honestly don’t know.”

This amphipod is the fastest known species in water. The speediest land creature is a termite, which can bite at more than 250 km/h.

Palmer is currently spending time in Bamfield on Vancouver Island trying to find the source of a mysterious popping sound in the Pacific ocean. He believes it could be a follow-up to this study, which was funded partially by the United States’ Office of Naval Research.

“It’s clearly not a fish making them, but we have no idea what the animal is. It could be another amphipod,” he said.

LISTEN | Fast amphipods:

Radio Active5:40Fast amphipods

Scientists have discovered a crustacean that can accelerate as fast as a bullet! 5:40

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