Limulus polyphemus, the Horseshoe Crab. A primitive arthropod with fossil ancestors going back to the Cambrian. The lineage includes by the Jurassic fossils which look, but for some subtle differences, virtually like the modern form. The specimen shown here on a mudflat at Bellmar, NJ, is immature. It is digging into the sediment at low tide. New Jersey has the greatest abundance of horseshoe crabs in the world, as well as the largest individuals.