Fossil annelids used in this study. (a) Pygocirrus butyricampum MGUH31365; (b) Phragmochaeta canicularis MGUH3088; (c) ROM62927, undescribed polychaete from Marble Canyon; (d) Canadia spinosa USNM83929c; (e) Burgessochaeta setigera USNM198705; (f) Kenostrychus clementsi OUM C.29544 (top right), OUM C.29543; (g) Arkonips topororum UMMP 73795; (h) Mazopherusa prinosi; (i) Fossundecima konecniorum ROM47990; (j) Esconites zelus ROM47521; (k) Dryptoscolex matthiesae ROM48542. (a,b) Early Cambrian, Sirius Passet, North Greenland; (c–e) Middle Cambrian, Burgess Shale, British Columbia; (f) Silurian (Wenlock), Herefordshire; (g) Middle Devonian, Arkona Shale, Hungry Hollow, Arkona, Ontario; (h–k) Carboniferous (Pennsylvanian), Mazon Creek, Illinois. Images (f) and (g) courtesy of Mark Sutton and Derek Briggs, respectively. (Online version in colour.)