Sclerobionts on tubes of the serpulid Pyrgopolon (Pyrgopolon) deforme (Lamarck, 1818) from the upper Cenomanian of Le Mans region, France

Serpulid polychaetes are described as common encrusting organisms inhabiting various substrates, but very few studies deal with tube-dwelling polychaetes as substrates for encrusters and borers. Here we focus on Pyrgopolon (Pyrgopolon) deforme, a serpulid species common in the Cenomanian of Le Mans region which acted as small solid benthic islands for colonization by invertebrates on a soft sandy/marly bottom. A relatively rich assemblage of 88 individuals was studied surficially, 15 specimens were imaged with CT, and five specimens were prepared as vacuum epoxy casts. Borings found in the tubes show relatively low diversity; nevertheless, several different, recurring shapes were recognized. Borings of the ichnogenus Rogerella are among the best preserved. The examined tubes represent the second known case of interaction between boring barnacles (Rogerella tracemakers) and serpulid worms. Short shafts perpendicular to tube surfaces are attributable to Trypanites isp. Longer, irregularly meandering tunnels resemble another form of Trypanites isp., but usually display more than one opening, suggesting Maeandropolydora. Another boring is a drop-shaped chamber with a relatively large aperture and several narrower side openings. They can be preliminarily assigned to unicamerate entobians. Among sclerozoans, encrusting oysters and cheilostome and cyclostome bryozoan colonies are the most abundant groups. Other encrusters such as serpulid and sabellid worms and foraminifers are less common, infesting fewer than 10% of tubes. Due to the high density of infestation, random distribution of boreholes and lack of signs of repair of the penetrated tube walls by the host organism, post-mortem infestation of Pyrgopolon (P.) deforme is suggested.