The horseshoe crab (also known as the king crab), is a hard-shelled invertebrate found on the sea floor in warmer climates. Despite it's name, the horseshoe crab is not actually a crab (or crustacean) and is in fact more closely related to arachnids such as spiders and scorpions. There are four different species of horseshoe crab found inhabiting the warmer shallows off the coasts of India, Japan, Indonesia, the eastern USA, and the Gulf of Mexico. The horseshoe crab has a hard outer shell, five pairs of legs and a long, thin tail which the horseshoe crab uses for changing direction whilst swimming rather than as a defensive weapon.