The horseshoe crab is a marine arthropod that has existed for over 450 million years. It is not a true crab but belongs to a group called chelicerates, which also includes spiders and scorpions. Horseshoe crabs have a hard, rounded shell and a long, spiked tail called a telson. They are primarily found in shallow coastal waters and are known for their unique blue blood, which contains a substance that is crucial for detecting bacterial contamination. Horseshoe crabs play an important role in the ecosystem as both predators and prey. They feed on small invertebrates and are a food source for various birds and marine animals. Additionally, their blood is harvested for medical purposes, particularly in the production of the Limulus Amebocyte Lysate (LAL) test, which is used to ensure the safety of medical equipment and vaccines.