The horseshoe crab is a species of arthropod that has been around for over 450 million years. Its scientific name is Limulus polyphemus, but it is also known by its genus name, Limulus. The horseshoe crab is found in the Atlantic Ocean and along the coasts of the United States, Mexico, and Japan. It is an important species in the marine ecosystem, as its eggs provide food for many shorebirds.