The Rare Mediterranean Endemic Gastropod Heliacus jeffreysianus Associated with the Endangered Savalia savaglia Coral

Heliacus jeffreysianus (Tiberi, 1867) is one of the rarest and elusive gastropods of the Mediterranean Sea, known for little more than 10 specimens collected in over ∼150years. Its ecology and details of the association to its host and prey, the gold coral Savalia savaglia Bertoloni, 1819, a parasitic zoanthid, were only partially known until the data presented here. We documented the presence of cluster of specimens of H. jeffreysianus on the host, where they feed and reproduce. It is postulated that these clusters of specimens could only occur where this parasitic zoanthid forms dense aggregations. Although S. savaglia is already listed as Near Threatened (NT) species due to ongoing habitat reduction of and the impact of lost fishing gears, its associated mollusc has a conservation status Not Evaluated (NE), we suggest considering the coextinction risk in threat assessment, in order to match that of the host. In this way this imperiled mollusc should be immediately protected until a full assessment according to IUCN criteria has been applied.