Members of the 'worm-snail' family Vermetidae occur in temperate and tropical seas and have developed numerous highly unusual traits, including a gregarious cementing habit (making them important reef builders as well as nuisance species when transported globally) and a rapid rate of gene-order change. Their colonies also mark former sea levels, making them important indicators of sea level and climate change. While their potential as an environmental indicator and as a model system for studying gene order change is very high, their full potential has not been realized because of confusion concerning species delineations and relationships. This project uses a combined approach of morphology, molecules, and ultrastructure to discern relationships in the group, and will provide a stable classification, as well as new inferences about the tempo of diversification and historical geography of these species. The project involves extensive and interdisciplinary student training and will provide a collaborative platform for worldwide efforts in research and understanding of this diverse and important group of mollusks. The results will be widely disseminated through many media to a broad range of audiences, benefiting science education and conservation. Increased knowledge of this group will be particularly valuable for addressing questions about invasive species and sea level and climate changes.