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 p..., , # A 480-million-year-old parasitic spionid annelid

Dataset DOI: [10.5061/dryad.wwpzgmsxm](10.5061/dryad.wwpzgmsxm)

## Description of the data and file structure

#### Methods:

Fossil specimens were scanned using a SkyScan1273 (Bruker Corporation) micro-computed tomography (micro-CT) scanner at the Museum of Comparative Zoology Digital Imaging Facilities. The slab containing MCZ.IP.202864 and MCZ.IP.202865 was scanned with a 1mm copper filter with energy set at 130 kV/61 μA and an imaging pixel size of 44.41μm. The slab containing MCZ.IP.202859 to MCZ.IP.202863 was scanned with a 2mm copper filter with energy set at 130 kV/278 μA and an imaging pixel size of 35.63μm. The scan files were reconstructed as cross-sectional TIFF stacks in NRecon (Bruker Corporation) and visualized using Dragonfly software, Version 2021.1 for Windows. Comet Technologies Canada Inc., Montreal, Canada; software available at [https://dragonfly.comet.tech/](https://dragonfly.comet.tech/).

#### File Types:

Thi...,