The Atlantic horseshoe crab (Limulus polyphemus), also known as the American horseshoe crab, is a species of marine and brackishcheliceratearthropod. Despite their name, horseshoe crabs are more closely related to spiders, ticks, and scorpions than to crabs. It is found in the Gulf of Mexico and along the Atlantic coast of North America. The main area of annual migration is Delaware Bay along the South Jersey Delaware Bayshore.
Their eggs were eaten by Native Americans, but today Atlantic horseshoe crabs are caught for use as fishing bait, in biomedicine (especially for Limulus amebocyte lysate) and science. They play a major role in the local ecosystems, with their eggs providing an important food source for shorebirds, and the juveniles and adults being eaten by sea turtles.
This group of animals is also known as horsefoot, or saucepan. Some people call the horseshoe crab a “helmet crab”, but this common name is more frequently applied to a true crab, a malacostracan, of the species Telmessus cheiragonus. The term “king crab” is sometimes used for horseshoe crabs, but it is more usually applied to a group of decapod crustaceans.
Limulus means “askew” and polyphemus refers to Polyphemus, a giant in Greek mythology. It is based on the misconception that the animal had a single eye.
Former scientific names include Limulus cyclops, Xiphosura americana, and Polyphemus occidentalis.
It is the tail that earns this order its name Xiphosura, which derives from the Greek for “sword tail”.
Studies of microsatellite DNA have revealed several distinct geographic groups in the Atlantic horseshoe crab. While there is extensive mixing between neighbouring populations, primarily due to movements by males, there is little or no mixing between the US and isolated Yucatán Peninsula horseshoe crabs, leading some to suggest that a taxonomic review is necessary.