Background: The NW Aegean Sea has a complex topography, high quality waters, oligotrophic to eutrophic conditions, is connected with estuaries and wetlands, is of high ecological interest, harbours all the types of human activities and yet few researchers work on its marine biodiversity. With this study, the contribution to the knowledge of the Hellenic and Eastern Mediterranean gastropod biodiversity of the studied families is continued, and an expansion of the search in other substrates and deeper waters of the NW Aegean Sea with emphasis on the minor in size species during the period from October 2008 to January 2014. Results: Thirty seven species belonging to seven families (Cerithiopsidae, Fissurellidae, Phasianellidae, Scissurellidae, Siliquariidae, Skeneidae, and Triphoridae) were identified and their biodiversity was compared with the current checklists of marine gastropod molluscs for the Hellenic Seas based on previous surveys. In this collection of gastropods, one species (Emarginula decorata Deshayes, 1863) is a new alien for the Mediterranean Sea, 14 species are new for the Eastern Mediterranean Sea and 16 species are new for the Hellenic fauna (with the one above mentioned alien species included). The main identification characteristics and ecological information such as habitat, distribution, alien expansion paths to the NW Aegean Sea and origin of the species are given and discussed. Conclusions: The Hellenic gastropod biodiversity of the studied families was enriched with 37 new records for the N Aegean Sea, out of which 16 are new for Greece, 14 are new for the Eastern Mediterranean Sea while one (Emarginula decorata) is a new alien for the Mediterranean Sea.
