Atlantic Horseshoe Crab

Stuart Humphreys

Australian Museum

Australian Museum
Sydney, Australia

Atlantic Horseshoe Crab
Limulus polyphemus

The Atlantic Horseshoe Crab is one of four living species of horseshoe crab – the only remaining members of the Xiphosura, one of the oldest groups of marine arthropods. Despite the name, horseshoe crabs are more closely related to arachnids like spiders, ticks and scorpions than they are to crabs.

The armour of horseshoe crabs has been so successful that it hasn’t changed for hundreds of millions of years. The hard, curved plates protect the soft bodies of the crabs and make it difficult for predators to knock them over and expose their less protected underbellies. Horseshoe crabs are also able to regrow lost limbs.

Horseshoe crabs have a copper-based blood that contains a substance called Limulus amebocyte lysate. This substance coagulates when in contact with small amounts of bacterial toxins and is used in the medical industry to test if medical equipment is sterile and to detect bacterial diseases.

Distribution: east coast of North America to Gulf of Mexico and Yucatan Peninsula
Conservation status: Near Threatened
Evolutionary distinctiveness: not assessed


  • Title: Atlantic Horseshoe Crab
  • Creator: Stuart Humphreys
  • Publisher: Australian Museum
  • Rights: Australian Museum

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