This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. HIGHLIGHTS-Saxitoxin (STX) appeared to spread throughout the cytoplasm of Crassostrea gigas hemocytes.-STX induces a caspase-dependent apoptosis death of hemocytes that does not depend on ROS production.-GTX5, which is present in large amounts in A. catenella, was found to be the most toxic derivate against oyster hemocytes.-Hyalinocytes were found to be a hemocyte population highly responsive to this toxic stress. Abstract:Exposure of the toxin-producing dinoflagellate Alexandrium catenella (A. catenella) was previously demonstrated to cause apoptosis of hemocytes in the oyster species Crassostrea gigas. In this work, a coumarin-labeled saxitoxin appeared to spread throughout the cytoplasm of the hemocytes. PSTs, including saxitoxin, were also shown to be directly responsible for inducing apoptosis in hemocytes, a process dependent on caspase activation and independent of reactive oxygen species (