Merostomata /(?)/

Mer·o·stom·a·ta

Merostomata

prop. n. pl.
  1. A class of Arthropoda, allied to the Crustacea. It includes the trilobites, Eurypteroidea, and Limuloidea. All are extinct except the horseshoe crabs (Limulus) of the last group. See Limulus. (Zool.)