A 480-million-year-old parasitic spionid annelid

The Paleozoic fossil record provides unique insights into the evolution of life history traits through the direct preservation of interspecific interactions in deep time. However, evidence of direct interactions between different species is relatively rare even among localities with exceptional soft-tissue preservation. Here we provide evidence of parasitic organisms from the Fezouata Shale biota of Morocco. Seven specimens of the bivalve mollusk <i>Babinka</i> show highly characteristic, question mark-shaped shell borings consistent with those produced by modern and fossil parasitic spionid polychetes. This suggests that the spionid polychetes, or polychetes with behavior consistent with spionids, were present in the Early Ordovician, a significant biostratigraphic shift in their temporal origins from their accepted Devonian occurrence. Many unique life history strategies which were significant components of the Fezouata Shale biota remain undiscovered, despite the high concentration of taxonomic attention on the site.