As such, the exact eurypterid time of origin remains unknown. Though fossils referred to as "primitive eurypterids" have occasionally been described from deposits of Cambrian or even Precambrian age, they are not recognized as eurypterids, and sometimes not even as related forms, today. Some animals previously seen as primitive eurypterids, such as the genus "Strabops" from the Cambrian of Missouri, are now classified as aglaspidids or strabopids. The aglaspidids, once seen as primitive chelicerates, are now seen as a group more closely related to trilobites.