A new attachment trace of a verrucid barnacle on Pliocene bivalve shells, Santa Maria Island, Azores

A new attachment trace belonging to the ichnogenus Centrichnus has been recognized on bivalve shells in a Pliocene coquina of the Pedra-que-pica section in Santa Maria Island (Azores Archipelago). The new ichnospecies Centrichnus dentatus isp. nov. is characterized by an elliptical outline, bounded by a groove and/or a series of pits, and by having a more or less pronounced central to off-center depression surrounded by a flat area. Based on these new findings, the diagnosis of the ichnogenus Centrichnus is emended, as is the diagnosis of the ichnofamily Centrichnidae. The new trace fossil was produced by the barnacle Verruca spengleri, which was found in direct association with the trace. Some specimens of Centrichnus dentatus isp. nov. were found cross-cut by phoronid borings (Talpina isp.) or clionaids sponge borings (Entobia isp.), and they co-occur with polychaete borings (Maeandropolydora isp.) and bivalve borings (Gastrochaenolites isp.). The traces belong to the Gnathichnus ichnofacies, which refers to the early colonization of hard substrates taking place within months, even though the recorded ichnocoenoses suggest longer exposure and colonization by several generations of cirripeds, lasting several years rather than months.