Paleozoic shell-Boring Annelids and their Trace Fossils

Polychaete shell-borings are widespread but not often common in Paleozoic strata of most continents, occurring in pelecypod, gastropod, cephalopod, coral, stromatoporoid, crinoid, brachiopod, ectoproct, and calcareous algal skeletons of Ordovician to Permian age. Four genera are known: Vermiforichnus (Spionidae), Ordovician to Permian; Caulostrepsis (Spionidae), Devonian to Oligocene; Myzoslomites (Myzostomidae), Ordovician to Jurassic: and possibly Conchotrema, Devonian to Permian. The Silurian Citonia sipho is a worm-boring, not a calcareous worm tube, referable to Vermiforichnus. An exceedingly well preserved Devonian fossilized polychaete, Vermiforafacta rollhisi, with complex setigerous parapodia, dorsal cirri, peristomial cirri, prostomium, and tentacle-like palps, occurs entombed in an agglutinated tube-lined worm-boring (Vermiforichnus). It may have been a shell-borer considering its many similarities to the spionid, Polydora, which apparently ecologically replaced it. Like Polydora, Vermiforafacta probably filtered food and sediment from sea water and constructed agglutinated tubes which lined its borings. In bivalves, borings parallel valves and are usually perpendicular to commissures; in massive skeletons, they radiate outward and laterally. Distorted later growth and “blisters” indicate that the host was often alive. Commensal to pathogenic parasitism existed and worms benefited from their hosts's feeding currents and protective shells. One polychaete nestler is reported. Life positions of hosts are sometimes indicated.