On the presence of elusive sea slugs and snails in the western Mediterranean (Mollusca: Gastropoda): new records

Citizen science provides us with much information about charismatic taxa such as the opisthobranchs, thus contributing enormously to enlarging the geographic distribution of species. This study collects new records of elusive sea slugs and snails in the Western Mediterranean coast (especially in the Catalan coast and the French Mediterranean coast) and contributes to new ecological information regarding phenology, diet, and behaviour. Out of the 36 species reported here, 20 correspond to new records in the Catalan coast (NE Spain), three are new records of pelagic pteropods for the Spanish coast, and 10 other species are new records for the French Mediterranean coast. All records have been registered at the online database of the NGO named Catalan Opisthobranch Research Group (GROC). This study highlights the importance of sampling at night and, especially, in shallow, often-understudied waters, which usually gather high species diversity. We believe the high-quality pictures and related species' information will serve future researchers and divers find and recognize these species in the Mediterranean basin.