Predatory gastropod drill holes in upper Miocene cold seep bivalves, Hokkaido, Japan

Many drilled specimens of Calyptogena pacifica and Conchocele bisecta were obtained from the upper Miocene Morai Formation in western Hokkaido. Thirty-three specimens of C. pacifica (19.8%) and four specimens of C. bisecta (9.3%) were drilled. This is the first report of drilling of cold seep bivalves by either fossil or Recent predatory gastropods. The shape of the holes suggests they appear to have been drilled by the co-occurring naticids Euspira and Cryptonatica. Only two holes might have been drilled by muricids. Ahnost all holes were completed other than two incomplete holes. Thus, effectiveness of armor (number of incomplete holes/total number of holes) is very low (0.06)