SSPECIES OF LIMULUS
At one time, there were many species of horseshoe crabs, however, only four have survived. Three of these can be found along the shores of Southeast Asia and nearby islands. The fourth species of the Horsehoe Crab is found in the waters of the North American continent. They range intermittently from the Yucatan peninsula in Mexico to northern Maine. Each major beach along the coast is believed to have a discrete horseshoe crab population that can be distinguished by adult size, Shell 

color, and eye pigmentation. Check out a map of the world showing where all four species are located.

Along the Atlantic coast, horseshoe crabs are most abundant between Virginia and New Jersey with Delaware Bay at the epicenter of the species distribution.

Horseshoe crabs are bottom-dwelling organisms that belong to the largest group of all living animals, the phylum known as arthropods. The presence of chelicera (pincer-like appendages), 5 pairs of walking legs and book gills, and lack of jaws and antennae make horseshoe crabs more similar to spiders, ticks and scorpions than to "true" crabs. Within the diversity of arthropods, horseshoe crabs have their own class called “Merostomata”, meaning “legs attached to the mouth”.

Of the four species of horseshoe crabs that exist today, all have a similar ecology and morphology. Taxonomic Classification of the Horseshoe Crab (Limulus polyphemus)