Plicopurpura patula and Monoplex parthenopeus (Gastropoda: Caenogastropoda): New evidence of the tropicalization of the Bay of Biscay (NE Atlantic)

Recent changes in climate and oceanographic conditions have been affecting the dynamics and composition of species communities worldwide, increasing the occurrence of tropical-subtropical species within a specific biogeographic area. This phenomenon defined as tropicalization is occurring in the Cantabrian Sea (Bay of Biscay), a transitional zone between two different regions of the North Atlantic. In this study we present new records of the tropical-subtropical gastropod species Plicopurpura patula and Monoplex parthenopeus in the European Atlantic, which constitute their northernmost distribution in the Atlantic Ocean to date. We provide a detailed characterization of both species, combining morphological and molecular features. Finally, supported by provided evidence and justification, we propose both species as two new potential bioindicators of the tropicalization phenomenon in the North Atlantic waters.