Zacanthoides is an extinct Cambrian genus of corynexochid trilobite. It was a nektobenthic predatory carnivore. Its remains have been found in Canada, Greenland, Mexico, and the United States. Its major characteristics are a slender exoskeleton with 9 thoracic segments, pleurae with long spines, additional spines on the axial rings, and a pygidium that is considerably smaller than its cephalon.