Asteroidea (Star Fish)
Amoebocytes are the main effector cells of the echinoderm immune system. In starfishes, a taxon in which bacterial diseases have been rarely reported, amoebocytes are considered to be the only circulating and immune cell type. Cells from the axial organ of the starfish. revealed the presence of cells resembling the lymphocytes of the vertebrates, as well as phagocytic, peroxidase positive cells. The lymphocyte-like cells have a high nucleo-cytoplasmatic ratio. In the starfish, a primitive immune system with characteristics resembling those of the immune system of vertebrates. In starfishes, a taxon in which bacterial diseases have been rarely reported, amoebocytes are considered to be the only circulating and immune cell type.