Ghost crabs can produce an angry growl with teeth in their STOMACH that they evolved to digest food
- Atlantic ghost crabs are known to make noise with their claws
- However, they can also make a mysterious rasping sound independently of this
- Experts used lasers to find out where the sounds came from in the crabs
- The sounds are made internally by rubbing teeth in the stomach grinder of their forehead
When threatened, Atlantic ghost crabs can make growling noises with the help of teeth in their stomach that they originally developed to help them break down food.
The crabs had long been known to make rasping noises by rubbing their claws, but the source of the mysterious internal noises was not clear.
Researchers used lasers and x-rays to determine where in the crab bodies the sounds were generated and revealed the responsible grinding mechanism.
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When threatened, Atlantic ghost crabs can make growling noises with the help of teeth in their stomach that they originally developed to help them break down food
When they are aggressive or protect their territory, ghost crabs are known to produce noise by bending one of their claws to rub on themselves, causing a lumpy part of the upper claw to move further down against a comb.
However, the crabs can also make grating sounds without using their claws – such as when defending their burrow or food up close, at which time they usually protrude their claws as a form of visual representation.
To find out how they do this, marine biologist Jennifer Taylor from the University of California, San Diego and colleagues studied 30 Atlantic ghost crabs – or Ocypode quadrata – in a laboratory setting.
The researchers used a technology called laser Doppler vibrometry – which measured vibrations with reflected laser light – to determine where in the crab the mysterious sounds were generated.
After finding that the sounds came from the crab digestive system, the team then used X-ray imaging to reveal the noise-making mechanism.
Researchers discovered that the sounds came from the so-called & # 39; stomach mill & # 39; from the crabs, teeth in the foreleg of the crustaceans that help them break down food.
The team discovered that the crab's stomach mill contains lateral teeth with a series of comb-like structures that can rub against the center tooth of the mill.
This produces sounds, with primary frequencies of less than 2 kHz, that the crab can control and vary during arguments.
It is unusual for animals to develop two independent mechanisms to create similar sounds that serve both defensive purposes, the researchers note.
& # 39; The stomach mechanism, however, has the advantage of releasing the claws for display and aggressive actions & # 39 ;, she added.
The full findings of the study were published in the journal Proceedings of the Royal Society B: Biological Sciences.
The crabs had long been known to make grating sounds by rubbing their claws, but the source of the mysterious internal sounds was not clear
WHAT DO WE KNOW OF ATLANTIC GHOSTWOOD?
Atlantic ghost crabs are small, yellow or gray crustaceans that grow up to 5 cm wide.
They are found along the Atlantic coast of America, from Massachusetts to southern Brazil.
They live in caves in the sand.
They are mostly earthly, but must periodically return to the sea to moisten their gills.
They have stalked, compound eyes that can turn around, giving them 360 ° visibility.
When they are aggressive, ghost crabs can produce noise by bending one of their claws to rub themselves.
New research has shown that they can also make growling noises with the help of their internal teeth that they have developed to better break down food.
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