Sea slug night fever: 39 new records of elusive heterobranchs in the western Mediterranean (Mollusca: Gastropoda)

Citizen (or community) science has provided copious and valuable information about charismatic marine taxa such as heterobranch gas- tropods, thus contributing enormously to the known geographic dis- tribution of many sea slug species. This study reports new records of elusive sea slugs in the coastal western Mediterranean (especially on the Catalan and French Mediterranean coasts) and contributes to new ecological information regarding their phenology, diet and behaviour. Out of 39 species reported here, 23 are new records for the Catalan coast (NE Spain), three are new records of pelagic pteropods for the Spanish Iberian coast, and eight are new records for the French Mediterranean coast. With 25 species found active at night, this study highlights the importance of sampling at night and in shallow, often under-sampled waters with high species diversity. Shallow waters usually have less diving activity and are harder to survey with heavy scuba equipment. We believe that the high-quality photos herein and the related species information will enable researchers, divers and the community to find and recognise these rare species in the Mediterranean basin