Limuloidea :: Limuloidea (n. pl.) An order of Merostomata, including among living animals the genus Limulus, with various allied fossil genera, mostly of the Carboniferous period. Called also Xiphosura..
Limulus :: Limulus (n.) 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..