any marine chelicerate arthropod of the genus Limulus, of North America and Asia, having a rounded heavily armoured body with a long pointed tail: class Merostomata
Also called: king crab
horseshoe crab in American English
US
any of an order (Xiphosura, class Merostomata) of sea arthropods shaped like thebase of a horse's foot and having a long, spinelike tail