UPPER CAMBRIAN STEM-LINEAGE CRUSTACEANS AND THEIR BEARING UPON THE MONOPHYLETIC ORIGIN OF CRUSTACEA AND THE POSITION OF AGNOSTUS

Three new arthropods in uncompressed condition have been discovered in Upper Cambrian limestone nodules (Orsten) of Vastergotland, Sweden. Together with Martinssonia elongata Muller & Walossek, 1986, they are recognized as descendants of early offshoots from the stem-lineage of Crustacea. Their morphology provides new insights into the evolutionary path and progressive development of ground plan characteristics along the stem-lineage and gives further support for the monophyletic origin of Crustacea s. str., which embraces all taxa with extant derivatives. Structures of the ventral morphology shared between these stem-lineage crustaceans and Agnostus lead to the consideration of alternatives for the currently assumed position of agnostids.