Terebellid Polychaete burrows from the Lower Palaeozoic

Trachyderma, as established by Phillips for specimens from the Upper Silurian of the Welsh Borderland, was triply preoccupied. Chapman described supposedly congeneric material from the Silurian of Victoria, but that material is generically distinct and Keilorites Allan was erected to accommodate it. Oikobesalon nom. nov. is erected as a replacement name for Trachyderma Phillips, which has been regarded variously as either a body fossil or a trace fossil. Based on its distinctive structure, it is interpreted here as the thin organic lining of a terebellid polychaete dwelling burrow. New illustrations and descriptions are given both of Phillips' original specimens and of O. citrimorion from England and Canada. Chapman's material of Keilorites is also redescribed to include burrows with a thick sediment wall. Putative gill plumes of Keilorites described by Chapman in a later paper are reinterpreted as ichnofossils comparable with certain Zoophycos. Unlike typical modern terebellids, the agent responsible for Oikobesalon may have been able to produce a new burrow after exhumation, or when required during growth. This capacity explains the morphological contrasts between Oikobesalon and previously described terebellid burrows.