A New Contribution on the Sea Slug (Gastropoda: Heterobranchia) Fauna of the Ustica Island Marine Protected Area (Lower Tyrrhenian Sea, Mediterranean)

Ustica is a Sicilian island for which most of the information available on the informal group of sea slugs comes from old and non-specific studies. Consequently, the aim of this study is to provide an updated list of the sea slugs of the Ustica Island Marine Protected Area (MPA). This study, carried out using the “photographic capture technique” in two surveys (early autumn and late spring), led to the finding of 32 species and 14 families of sea slugs. Overall, considering both the literature and current data, a total of 77 species and 33 families of sea slugs have been documented on this island. While these numbers might indicate high species richness compared to other previously investigated Sicilian islands, they might also reflect the fact that Ustica Island is the only one for which numerous malacological studies have been performed.