Horseshoe crabs are ancient, having early ancestors which date back over more than 400 million years ago. Though these are commonly mistaken as member of the crab family, they are closely related to arachnids (scorpions, spiders, etc.) than to crustaceans. Mangrove horseshoe crabs are mostly found in Southeast Asia and Some parts of America. They are known for their large nesting groups on beaches. Female horseshoe crabs are about 1/3 bigger than male. These arthropods are important to the medical industry. They don’t have hemoglobin in their blood but instead rely on hemocyanin to carry oxygen throughout their body. Unlike humans who have white blood cells to fight off bacteria, the horseshoe crab use amebocyte. This blood substance solidifies when toxins are detected, trapping the threat in a blue, jelly-like substance.