Drill hole predation on fossil serpulid polychaetes, with new data from the Pliocene of the Netherlands

The fossil record of drill holes in shelled invertebrates is primarily focused on bivalves and gastropods as prey. This study shows by means of an examination of serpulid polychaetes from the Pliocene of Langenboom (The Netherlands) and a review of the literature that drill holes could be much more common in fossil tube-bearing serpulid polychaetes than previously known. A study on a population of 915 specimens of Ditrupa cf. arietina shows that > 18.6% and b 62.1% of the Langenboom population was drilled using four methods, three of which are introduced herein. These new methods for serpulids can be used for fragmented scapho-pod faunas as well in future studies. Drill holes in specimens from Langenboom were primarily caused by naticid gastropods, suggesting that Ditrupa cf. arietina had an infaunal lifestyle. In contrast to earlier results for serpulids, drill holes were randomly positioned with respect to the side of the tube. In general, it appears that Ditrupa spp. and scaphopods are mainly drilled in the middle part of the tube regardless of tube length, which suggests that naticids were able to locate the tissue inside the tube when the animal had withdrawn into its tube. The drill holes in serpulids were smaller than those for a bivalve assemblage from the same beds; the drill hole sizes in serpulids are statistically comparable to those of the small bivalve species Corbula gibba and Digitaria digitaria from the same fauna with an average width of nearly 6 mm. The latter suggests that Ditrupa cf. arietina was mainly drilled by small, potentially juvenile naticids. Not only does this study ad-dress drill hole predation on serpulids through time and their paleogeography, but it also elucidates naticid behavior in selecting a drill hole site on cylindrical tubes. More work should be done on drill holes in fossil serpulids, which may reveal a rich history of drilling on serpulids. In studies that assess the overall impact of drill hole predators on the benthic fauna, serpulids, if common, should be taken into account as well besides mollusks.