Atlantic Horseshoe Crab – Limulus polyphemus

Tags: Invertebrate, Ocean, arthropod

Atlantic Horseshoe Crab

Atlantic Horseshoe Crab

An adult Atlantic horseshoe crab on a beach Bill Perry, U.S. Fish and Wildlife Service
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What does an Atlantic horseshoe crab look like?

The Atlantic horseshoe crab has 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 breathe with “book gills”. Horseshoe crabs grow to be about 24 inches long by 12 inches wide. They use their legs to move along and to tear up food and place it in their mouths.

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.

Where do Atlantic horseshoe crabs live?

Atlantic horseshoe crabs live in shallow and deep water. So you may find them on the ocean floor and along shore.

What do Atlantic horseshoe crabs eat?

Horseshoe crabs like to eat small clams, worms, detritus and invertebrates.

What are some interesting facts about Atlantic horseshoe crabs?

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 for fertilizer, chicken feed and pig feed. Sometimes fishermen use them as bait. Horseshoe crabs are also used in medical research. Something in their blood 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. Photo by Amy Freeman


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