An ancient species, the horseshoe crab (Limulus polyphemus) is often referred to as a "living fossil." The horseshoe crab as we know it today has inhabited our oceans for almost 350 million years. It is classified with crabs (phylum Arthropoda), but it is not actually a crab or even a crustacean. It is a benthic (bottom-dwelling) predator that uses its small pinchers to pick through the sand for clams, worms and other critters that make up its diet. Each spring, mature horseshoe crabs spawn in shallow coastal areas where their eggs serve as a critical food source for migrating shorebirds. The Atlantic horseshoe crab, one of only four horseshoe crab species worldwide, is found in coastal areas from Maine to the Yucatan peninsula.