Bivalve mollusks are among the most important members of benthic communities for their environmental impacts and commercial value. Infectious diseases have caused severe mortalities in bivalves such as the Eastern oyster, leading to significant alterations of ecosystem health. For most bivalve diseases, however, little is known about the dynamics of pathogen transmission, including basic information such as the routes and the mechanisms of infection or the factors that facilitate or inhibit the entry of pathogens into their hosts. Interestingly, recent studies demonstrated that pathogens (namely Perkinsus marinus the causative agent of Dermo disease in oysters) can subvert host defense factors (e.g. galectin) to gain entry in oyster blood cells and initiate infections. This collaborative effort will unite the expertise and facilities of specialists from Stony Brook University and the University of Maryland, providing a synergistic approach to determine how infectious agents hijack host defense factors associated with pallial tissues (mantle, gills) to initiate infections in the Eastern oyster. These studies on cellular and molecular host-pathogen interactions will address long-standing questions regarding mechanism(s) by which marine microbes colonize and invade bivalves. This new information is urgently needed to target future investigations to innovative strategies for disease mitigation. Beyond the specific case of oyster diseases, this project would have a fundamental impact on how scientists view initial encounters between microbes and their marine invertebrate hosts, and has the potential to lead to the development of new research approaches. From the educational standpoint, a primary objective of this project is the multidisciplinary training of graduate, undergraduate, and high school students and teachers, including underrepresented minorities, in the pathology and immunology of marine organisms. The products from research and educational activities will be disseminated by scientific electronic and printed media, including graduate dissertations and teaching modules for the classroom, as well as publications in shellfish trade magazines and fact sheets directed at stakeholders and the general public.