Horseshoe crab

Horseshoe crab, or king crab, any of several marine arthropods of the order Xiphosura, “living fossils” whose almost identical ancestors have been found in rocks 175 million years old. King crabs are not true crabs but are more closely related to spiders. If the dome-shaped shell is turned over it shows a horseshoe outline and a series of jointed legs. King crabs live near sheltered shores on the Atlantic coast of the United States and around the coast of Asia. In some places king crabs are fished for pig and chicken feed, and fertilizer. They are pests in clam beds.