(1) For this interesting animal, extensive morphological and developmental biological studies have been conducted, but limited information has been available on endocrinology and physiology of amphioxus .(2) The cephalochordate amphioxus is the closest living invertebrate relative of the vertebrates and therefore the best model organism for understanding the composition of the ancestral chordate genome.(3) A few years ago, some molecular embryology data on amphioxus have revived the long forgotten hypothesis that the ancestor of coelomates was a segmented animal.(4) Organisms along the lines of the cephalochordate amphioxus use the gill apparatus for filter feeding.(5) Thus amphioxus is the only chordate species in which distinct insulin and IGF genes have not been found.
