A 480-million-year-old parasitic spionid annelid

The Paleozoic fossil record can provide 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, with most examples being known from
Cambrian marine deposits. Here we provide the first evidence of parasitic
organisms from the Fezouata Shale biota of Morocco, the most diverse and
abundant Ordovician site with exceptional preservation, but that has
heretofore shown no evidence for parasitism. Seven specimens of the
bivalve mollusc Babinka show highly characteristic, question mark-shaped
shell borings consistent with those produced by modern and fossil
parasitic spionid polychaetes. Our results include anatomical and
quantitative comparisons with modern and fossil spionid borings and
underscore two major conclusions. The first is that the spionid
polychaetes were present in the Early Ordovician, which evidences a
significant biostratigraphic shift in their temporal origins from their
accepted Devonian occurrence. The second is that many unique life history
strategies, which were significant components of the Fezouata Shale biota,
remain undiscovered, despite the high concentration of taxonomic attention
the site has received.