horseshoe crab

Marine arthropod of the order Xiphosura, class Merostomata, distantly related to spiders, which lives on the Atlantic coast of North America and the coasts of Asia. The upper side of the body is entirely covered with a rounded shell, and it has a long, spinelike tail. Horseshoe crabs grow up to 60 cm/2 ft long. They crawl along the bottom in coastal waters and lay their eggs in the sand at the high water mark.