merostomata
Mer`o*stom"a*ta, n. pl. Etym: [NL., fr. Gr. (Zoöl.) Defn: A class of Arthropoda, allied to the Crustacea. It includes the trilobites, Eurypteroidea, and Limuloidea. All are extinct except the horseshoe crabs of the last group. See Limulus.