The only existing genus of Merostomata. It includes only a few species from the East Indies, and one (Limulus polyphemus) from the Atlantic coast of North America. Called also Molucca crab, king crab, horseshoe crab, and horsefoot.

amebocyte lysate: Product of white blood cells of the horseshoe crab used in an assay for endotoxin.

type genus of the family Limulidae