Abstract

Marine bivalve mollusk defensive system includes hemocytes, the circulating blood cells which are actively engaged in the defense and other physiological processes. This review comprehensively summarizes the current knowledge about hemocytes in marine bivalves, with a primary focus on their immune and non-immune functions. Marine Bivalve hemocytes broadly classified into granulocytes and hyalinocytes, mediate cellular defense through phagocytosis, encapsulation, and secretion of enzymes and reactive oxygen species (ROS). Beyond immunity, they participate in wound healing, shell formation, and nutrient transport, showcasing their diverse and intriguing roles. Recent studies that combine hemocyte subpopulation characterization with functional assays have revealed their versatility. However, challenges persist in establishing a unified nomenclature across species. Environmental factors significantly influence hemocyte populations, highlighting their potential as bioindicators. While significant progress has been made, gaps remain in understanding hemocyte sub-population dynamics and non-immune activities. This review underscoresthe need to consider hemocytes in the broader context of environmental and whole-animal physiology, suggesting future research directions in molecular mechanisms, host-pathogen interactions, and aquaculture applications.