Innate immunity is an ancient defense mechanism that operates in multicellular organisms to detect and eliminate pathogens and distinguish self from non-self. Animal immune cells deploy diverse behaviors during pathogen elimination, including phagocytosis, secretion of inflammatory cytokines, and expulsion of nuclear material - the casting of extracellular DNA “traps” (e.g. ETosis). Hemocytes are circulatory cells in bivalve mollusks and are reported to have roles in immunity, biomineralization, and nutrient transport. A thorough understanding of hemocyte cell types and their discrete or overlapping functions is critical for assessing bivalve responses to pathogen challenge and other physiological processes. However, current resources describing hemocyte types and their associated function are often conflicting or vague, making interpretation of specific cellular immune responses to infection challenging. We have applied flow cytometry, microscopy, and biochemical approaches to explore immune cell behaviors and hemocyte transcriptional signatures in the Pacific oyster (Crassostrea gigas). Our findings suggest a variety of cell types may be competent for a range of anti-microbial responses, including ETosis. We also find that some immune cell type behaviors may be activated by non-canonical signaling pathways. These data provide an opportunity to explore both conserved and novel aspects of pathogen defense mechanisms associated with shellfish innate immunity.