Transparent helmet protects click crabs from their own impacts

(ORDO NEWS) — By snapping their combat claws, some crustaceans strike the enemy with a super-powerful acoustic blow, from which they themselves are protected by a transparent “helmet” with a hole in the front.

Clicker shrimp make some of the loudest noises in the ocean, deafening fish as they swim by. However, they remain immune to their own sonic shocks.

Scientists have found that reliable protection is provided by a transparent “cap” that covers the surroundings of the eyes. Its unusual structure effectively dissipates impact energy and could form the basis for the development of safer helmets.

Miniature click crabs grow to only a few centimeters, but they can compete with beluga and sperm whales for the title of the loudest inhabitants of the sea; their accumulations interfere with the operation of underwater sonars.

These sounds are produced by an asymmetrical combat claw with a highly unusual device. The combination of solid and elastic parts allows you to “cock” it and release it sharply, like a catapult. This creates a powerful shock wave that creates a deafening click and even short flashes of light.

It is believed that the shrimp themselves use these sounds to communicate with each other, as well as for hunting, stunning prey swimming by. In addition, it is shown that due to global warming and warming of the water, crustaceans become more active and in recent years click even louder than before.

However, a blow of such force can be dangerous for the clickers themselves, especially for their nervous system. The mechanisms of their protection were investigated by Alexandra Kingston and her colleagues from the American University of Tulsa.

Transparent helmet protects click crabs from their own impacts 2
Shrimp Alpheus heterochaelis (A), its fighting claw (B) and “orbital cap” (C), the boundaries of which are shown by a dotted line, and the anterior opening is shown by an arrow

The main attention of scientists was paid to the transparent “orbital cap” (orbital hood) – something like a tiny helmet that covers the upper part of the cephalothorax of click beetles – the area around the eyes.

This structure is found only in them, but not in other crustaceans. To verify its protective function, scientists set up experiments with crayfish Alpheus heterochaelis , some of which had a protective helmet removed and then subjected to a sonic boom.

Transparent helmet protects click crabs from their own impacts 3
Graphic description of the new work

Normally, animals are frightened by such exposure and try to return to the shelter. Ordinary shrimp with an “orbital cap” did just that.

However, those who had it removed behaved completely differently: they began to spin and fall, became disoriented and had difficulty controlling their body, and it took seven times longer to get to shelter than their neighbors who retained protection of the head ganglia.

The “orbital cap” does not fit snugly against the rest of the crayfish exoskeleton. Being transparent, it covers the eyes, and the space between them and the “helmet” is filled with water. In addition, it opens with a hole in the front.

Scientists believe that it is this structure that provides the necessary protection: a sharp concussion of the “helmet” is transmitted to the water, but the resulting excess pressure is ejected through the opening in front. Perhaps this structure will also improve the helmets that people use.


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