Atlantic Horseshoe Crab

Scientific Name: Limulus polyphemus

Atlantic Horseshoe Crab

An adult Atlantic Horseshoe Crab on a beach Bill Perry, U.S. Fish and Wildlife Service
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Atlantic Horseshoe Crabs have a large protective shell. They have long spine-like tails and ten legs. Their shells are tan to dark brown and their legs are dark reddish brown with white markings. They have “book gills” that they use for breathing. Their average size is 24 inches long by 12 inches wide.

Atlantic Horseshoe Crabs live in shallow and deep water. They can be found on the ocean floor and along shore. They use their legs to move along and to tear up food and place it in their mouths. Horseshoe crabs like to eat small clams, worms, detritus and invertebrates.

Horseshoe crabs are actually more closely related to spiders, ticks and scorpions than they are to other crabs. The shell of the horseshoe crab protects it from predators. They use their tails like rudders as they walk along the ocean floor. The tail also helps them to flip over when they are upside down.

You may have heard horseshoe crabs referred to as living fossils. This is because they are one of the most primitive arthropods. They existed in their present form as far back as 360 million years ago!

People once used horseshoe crabs fro fertilizer, chicken feed and pig feed. Today they are sometimes used as bait. They are also used in medical research. There is something in their blood that reacts to bacteria that are harmful to humans. This stuff in their blood is used to test medical equipment that will come into contact with human blood, to make sure the medical equipment isn’t contaminated with bacteria. The population of Atlantic Horseshoe Crab is threatened by pollution, habitat destruction and harvesting for medical research.

Additional Images:

Atlantic Horseshoe Crab

Dave with an Atlantic Horseshoe Crab molt Amy Freeman

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