DO NATICID GASTROPODS LEAVE PREDATORY MICROTRACES WHEN THEY DRILL THEIR BIVALVE PREY?

Previous studies on the interaction of the muricid gastropod, Nucella, and its mussel prey, Mytilus, have reported that mechanically produced radular rasping microstraces located on the walls of drill holes could be used confirm their predatory origin in the fossil record where the identity of the trace maker is less certain. Here, we expand upon this study to determine whether three genera (Euspira, Neverita, Sinum) in the family Naticidae also leave diagnostic features on their bivalve prey. Naticids were fed bivalve prey from four families (Mytillidae, Veneridae, Donacidae, Myidae) under experimental lab conditions. Each resulting drill hole from a predator-prey interaction was imaged under ESEM on a JEOL Neoscope JCM 5000 to detect microtraces. Each prey specimen was graded according to whether microtraces were present, potentially present but unclear, or absent. Microtraces were determined to be present and predatory in origin based off of a series of established criteria including, but not limited to: rasp mark or trace orientation relative to the shell microstructure, trace length and width, and frequency of potential traces. Preliminary results suggest that the three naticid genera do not leave predatory microtraces as often as was reported for Nucella (<10% vs. 74.29% of drillholes, respectively). This difference in the prevalence of microtraces may be due to anatomical differences between gastropod families. In particular, the accessory boring organ in naticids is located under the tip of the proboscis rather than near the pedal gland or in the sole of the foot in muricids. Consequently, it is possible that acid secretions from the naticid accessory boring organ may more readily erase rasping microtraces than those from muricids during the drilling process, which limits their utility to confirm the predatory origin of drillholes produced by naticids in the fossil record.