Instead they regarded Opabinia's lobe+gill arrangement as an early form of the arthropod limbs before it split into a biramous structure.[7] However, this similar chemical composition is not only associated with the digestive tract; Budd and Daley (2011) suggest that it represents mineralization forming within fluid-filled cavities within the body, which is consistent with hollow lobopods as seen in unequivocal lobopodian fossils.