The horseshoe crab (family Limulidae) is a strange creature that remains a fascinating topic for scientists everywhere. They are not “crabs”, but living fossils. Today, they still resemble their Jurassic relatives. They are some of the favorite food items of sea turtles along the East coast.
There are five pairs legs under the horseshoe-shaped body. All but the last set end in small claws that help the animal move and eat. Speaking of which, where is the mouth? At the base of the legs, near the center of the animal, there are small spines that act like teeth and help the horseshoe crab chew before the food enters the mouth.
Despite being known as horseshoe crabs, they are actually more closely related to spiders and scorpions, and are in the subphylum Chelicerata. In fact, a spider’s fangs are remarkably similar in structure to the first set of legs on the horseshoe crab; these are called “chelicerae” in both cases.
Horseshoe crabs have blue blood that is frequently used in pharmaceuticals. Their blood clots if it comes into contact with remnants of bacteria, and can be used to test the safety of medicines.