ABSTRACTNumerous spherical bodies containing electron‐dense material, fibrous material, and membranous material are present in the cytoplasm of two dinoflagellate species,Prorocentrum lima(Ehr.) Dodge andProrocentrum maculosumFaust. Similar bodies have been observed in other dinoflagellates and have been termed accumulation bodies or PAS bodies. In bothProrocentrumspecies, these bodies autofluoresce under blue light excitation and increase in size with cell culture age. They possess acid phosphatase activity, react positively with the periodic acid/Schiff reagent, and stain with acridine orange. All these properties are characteristic of eukaryotic lysosomes; thus, we propose that dinoflagellate accumulation bodies and PAS bodies are identical organelles and are, in fact, dinoflagellate lysosome