The axial organ of the sea star Asterias rubens (Asterid) is a primitive immune organ. The B-like cells, when stimulated by various antigens, produce antibody substances correlating with ig kappa genes. On the other hand, component complement genes were found. For each component, one or several contigs were analysed. It is said that Asterias forbesi, another sea-star, in earlier results, showed complement-like activity. A brief comparison with the complement system in sea urchin (Echinid) was performed, especially about the C3 component.
