We investigated the developmental expression pattern of AmphiCAM in cephalochordate amphioxus (Branchiostoma belcheri tsingtauense) We cultured and sampled the animals at different developmental stages (eggs and larvae), and used in-situ hybridization and northern blotting to document the spatial and temporal changes in AmphiCaM expression The alimentary tract dominates the development from the late neurula stage to the adult stage AmphiCaM expression increased significantly in the alimentary tract during the late neurula stage and remained elevated in the adults Our results indicate that AmphiCaM is involved in the differentiation of the alimentary tract in amphioxus, and furthermore, provide an insight into the change in function of CaM genes during evolution