hemocytes

Hemocytes are the cellular component of the hemolymph—the circulating fluid in the open circulatory systems of many invertebrates, especially arthropods (insects and crustaceans), mollusks, and echinoderms. They patrol the body cavity, participate in innate immune defenses, and contribute to tissue repair and homeostasis. Hemocytes originate from hematopoietic tissues and differentiate into several cell types; classification varies among groups, and exact naming is not universal.

In insects, commonly recognized hemocyte types include prohemocytes (precursors), plasmatocytes (the principal phagocytes and peptide producers), crystal cells (melanization enzymes and clotting components), and lamellocytes (specialized for encapsulating large foreign bodies). In crustaceans, hematocytes are often grouped as hyaline cells and granulocytes, which perform phagocytosis, nodulation, encapsulation, and participation in the phenoloxidase–melanization system. Across mollusks and echinoderms, hemocytes likewise mediate phagocytosis, wound closure, and antimicrobial responses, though cell morphologies and markers differ by lineage.

Functions commonly attributed to hemocytes include phagocytosis of microbes and debris, encapsulation of larger invaders, production of antimicrobial peptides, participation in clotting and wound repair, and activation of melanization to confine pathogens. Studied as a model of invertebrate innate immunity, hemocytes are a focus in research on host–pathogen interactions and environmental stress responses.