Since the description of the first cycloid from the Carboniferous of Yorkshire, England (Phillips, 1835) the Cycloidea have been placed in many different groups within the Arthropoda. These include agnostid trilobites (Phillips, 1835), xiphosure merostomes (Packard, 1872; Oosterink, 1978), limuloid-like crustaceans (Woodward, 1905), decapod brachyurans (Trauth, 1918), branchiurans (Hopwood, 1925), copepods (Clark, 1989), and maxillopodan crustaceans (Schram et al., 1997).