The immunity in bivalves is based on: cells of the immunodefense syste
m (the hemocytes), enzymes found in serum and hemocytes and humoral fa
ctors involved in communication between hemocytes themselves and hemoc
ytes and tarjet. Non specific defense mechanisms imply phagocytosis, e
ncapsulation, enzymatic destruction and cytotoxicity. The immune respo
nse shows a great variability depending on pathologic and physiologic
condition of bivalves and environmental conditions.