A New Arrival: First Record of the Genus Vayssierea Risbec, 1928 (Mollusca, Nudibranchia) in the Mediterranean Sea

Abstract Exploring the Nudibranchia diversity, a specialized group of gastropods, from ports and marinas revealed a powerful way to early detect Mediterranean non-indigenous species and to uncover overlooked endemic diversity. During a survey in the Port of Civitavecchia, Rome, Italy (Tyrrhenian Sea), one specimen belonging to the neglected genus Vayssierea Risbec, 1928 was detected. Morphological and molecular analyses, based on the COI mitochondrial marker, confirmed it belongs to this Indo Pacific genus and they revealed Vayssierea sp. 1 is another case of challenging species identification. In fact, all the known species belonging to this genus share a similar external morphology and lack reliable diagnostic features, which make a comparison with the original descriptions of the species impossible, currently preventing identification at the species level. This is the first record of this genus in the entire Mediterranean Sea, and it highlights the importance of continuous monitoring of heavily human-impacted areas, such as ports and marinas, to early detect non-indigenous and/or neglected and overlooked taxa.