Abstract
The Mediterranean Sea is known for its rich biodiversity, which includes both indigenous and non-indigenous species. Libya a country with over 1700 km of coastline, is considered data poor, especially in regard to Heterobranchia which are well documented in other parts of the Mediterranean Basin. To fill this gap, a six-year project was undertaken to assess sea slug biodiversity in Libyan waters. As part of this project the southward spread of the non-indigenous species Godiva quadricolor was documented for the first time in Libyan waters found in a natural bay off the coast of Regatta (Tripoli). The proximity of the survey site to the large Tripoli Harbour suggests that shipping traffic may have been a probable way for its introduction. Additionally, the abundance of prey in the area could have favoured its introduction. Two indigenous sea slugs, Elysia timida and Caloria quatrefagesi were also documented for the first time in the same area. Elysia timida and C. quatrefagesi were used to assess G. quadricolor predation under laboratory conditions.