Horseshoe Crab - Classification

Classification

Horseshoe crabs resemble crustaceans, but belong to a separate subphylum, Chelicerata, and are more closely related to arachnids, e.g. spiders and scorpions. The earliest horseshoe crab fossils are found in strata from the late Ordovician period, roughly 450 million years ago.

Limulidae is the only recent family of the order Xiphosura and contains all four living species of horseshoe crabs:

• Carcinoscorpius rotundicauda, the mangrove horseshoe crab, found in Southeast Asia
• Limulus polyphemus, the Atlantic horseshoe crab, found along the northwest Atlantic coast and in the Gulf of Mexico
• Tachypleus gigas, found in South and Southeast Asia
• Tachypleus tridentatus, found along East Asian coasts