Horseshoe crabs are marine arthropods that live primarily in and around shallow ocean waters on soft sandy or muddy bottoms. They occasionally come onto shore to mate. They are commonly used as bait and in fertilizer.
Horseshoe crabs resemble crustaceans, but belong to a separate subphylum, Chelicerata, and are closely related to arachnids. The earliest horseshoe crab fossils are found in strata from the late Ordovician period, roughly 450 Mya, and are believed to be close relatives ...(more)