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Shrimps and Sonoluminescence

Mantis shrimp, or stomatopods, are carnivorous marine crustaceans of the order Stomatopoda, branching from other members of the class Malacostraca around 340 million years ago.

Mantis shrimps typically grow to around 10 cm (3.9 in) in length, while a few can reach up to 38 cm (15 in). A mantis shrimp's carapace (the hard, thick shell that covers crustaceans and some other species) covers only the rear part of the head and the first four segments of the thorax.

Varieties range in color from shades of brown to vivid colors, with more than 450 species of mantis shrimps being known.

They are among the most important predators in many shallow, tropical and subtropical marine habitats. However, despite being common, they are poorly understood, as many species spend most of their lives tucked away in burrows and holes.

Called "sea locusts" by ancient Assyrians, "prawn killers" in Australia, and now sometimes referred to as "thumb splitters" — because of the animal's ability to inflict painful wounds if handled incautiously — mantis shrimps have powerful raptorials that are used to attack and kill prey either by spearing, stunning, or dismembering. Some mantis shrimp species have specialised calcified "clubs" that can strike with great power, while others have sharp forelimbs used to seize the prey (hence the term "mantis" in its common name).

Mantis Shrimp
Mantis Shrimp © Wikimedia Commons

So, what links sonoluminescence and shrimp ? Mantis shrimps have incredibly strong claws. Those claws can move at around 100km per hour ! When that claw closes in water it produces a bubble. This is a very special bubble though; it’s called a cavitation bubble. Mantis shrimp can use these cavitation bubbles as a defence mechanism or to stun their prey. Here’s a video of a shrimp making some bubbles.

Whenever the pressure in a liquid suddenly drops, cavitation occurs. This physics phenomena can even break beer bottles. Cavitation bubbles are formed when the force from the shrimp’s claws causes a low pressure bubble of air to be formed within the water. The water around the bubble is at higher pressure. This difference of pressures causes the bubble to collapse. This is when all the interesting stuff happens.

The inside of the bubble becomes incredibly hot, estimates are that the temperature of the bubble can reach five to ten thousand Kelvin. This can be hotter than the surface of the sun. Blueish light has also been detected for mere trillionths of a second. The light and heat produced by the bubble is called sonoluminescence. Bubble dynamics and their stability are theorised to be responsible, but sadly scientists have not yet definitively proven how this sonoluminescence occurs.

Here's a video of a mantis shrimp hunting down its prey in an aquarium :

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