Horseshoe crabs have been on this planet for an estimated 450 million years, surviving ice ages, asteroids and more, and predating dinosaurs by more than 200 million years. Their populations are on the decline.
Horseshoe crabs are unique in a number of ways, including having 10 eyes and 10 legs, with a mouth in the center. And, despite their name, horseshoe crabs are not crustaceans like true crabs but, rather, are more closely related to spiders and scorpions. They belong to the Merostomata class, which means “legs attached to mouth.” These living fossils are a keystone species that play a valuable role in the environment, hosting organisms such as barnacles and blue mussels on their shells, acting as predators and helping to control clam, mussel and crustacean populations and providing a food source for a number of marine animals.