The post These Crabs Power-Wash Their Eyestalks — and We Can’t Stop Watching! appeared first on A-Z Animals.
Getting something in our eyes is irritating, both figuratively and literally. Other than flushing them with eye drops or water, there’s not much we can do without risking damage to our eyes. However, the corneas of crustaceans are made of chitin, the same material that makes up their hard exoskeletons. So, the clever self-cleaning method below won’t damage the eyes of the Atlantic ghost crab shared by goatsportspro. While this technique may not work for humans, it’s perfect for crabs … and car windshields.
The Atlantic Ghost Crab
Atlantic ghost crabs (Ocypode quadrata) prefer tropical and subtropical intertidal zones on the eastern coasts of North and South America. The crab is semi-terrestrial but well-adapted to life on land. When the tide goes out, they leave their burrows in the sand to hunt for clams and small crabs, especially at night. They only return to the water on occasion to wet their gills, as they can drown if underwater for too long. These crabs also extract water from wet sand. The fine hairs near the bottoms of their walking legs wick water up to their gills.
The Atlantic ghost crab is light yellow to greyish-white, helping it to blend in with its beach habitat. Their carapace length only reaches a maximum of about two inches. They have a total of five pairs of appendages. Four pairs of jointed walking legs allow them to move as fast as 10mph. The other pair of appendages are claws called chelipeds. These white claws are of unequal size, with the enlarged claw used for eating and burrowing. They also have large, black eyes on club-shaped eyestalks, but the males do not have horned tips like other ghost crab species.
The Eyestalks Have It
In addition to the Atlantic ghost crab, there are a number of semi-terrestrial crabs with eyes on eyestalks. Fiddler crabs, soldier crabs, and other ghost crab species have long, vertically oriented eyestalks that are set close together. Having eyes on stalks gives the crab a wider visual field. This adaptation also helps them determine depth and size in their relatively flat environments. Atlantic ghost crabs have a 360° field of view, and their corneas make up at least half of their eyestalks. However, their large eyes are sensitive to light, and they cannot see directly overhead.
Many crabs can retract their eyestalks into special grooves in their exoskeletons. This not only protects their eyes, but raising and lowering the eyestalks also helps to dislodge sand and dirt. Other crabs, such as the soldier crab, clean their eyestalks by rubbing their chelae, or pincers, all over these areas. Their maxillipeds, modified appendages used as additional mouthparts, vibrate to help remove debris as they clean. Fiddler crabs have comparable cleaning strategies to ghost crabs, but fiddler crabs use their eyes as extra appendages for grooming more often than ghost crabs.
The Atlantic Ghost Crab Self-Cleaning Method
Other crabs have similar strategies to remove objects that impair their vision, but the Atlantic ghost crab is unique in its almost mechanical precision. When the tide goes out and they climb up from their underground burrows, the crabs have been observed cleaning the sand from their carapace, mouthparts, and eyes. As we can see in the video, they lower their eyestalks into fitted grooves on either side of their carapace, the hard upper section of the shell. Retraction is thought to be caused by electrical impulses in nerve cells that control muscles in the eyestalks. With the eyes retracted into their grooves, the crabs use their maxillipeds like car windshield wipers to clear away the debris.
Specific grooming habits of the Atlantic ghost crab have not been extensively documented. However, scientists note that they frequently groom their eyes and maxillipeds with brushing or scraping techniques, such as the one as shown above. Researchers also found that ghost crab males groom less often than females. Another study determined that the crabs clean their eyes significantly less in the presence of other ghost crabs. Their eyestalks are often retracted for protection, but theories suggest that reducing grooming tasks avoids temporary vulnerability around potential rivals. Although the little crab above appears more interested in getting clean than looking tough.
The post These Crabs Power-Wash Their Eyestalks — and We Can’t Stop Watching! appeared first on A-Z Animals.