What Develops Into Gills? In jawless animals such as lampreys, gills form from the embryo’s innermost layer of cells, or ‘endoderm’, whereas in jawed vertebrates, including many fish species, gills were thought to develop from the outermost layer, or ‘ectoderm’. This led scientists to think that gills evolved separately in the two lineages. What structure
Are Ray Finned Fishes Jawed Vertebrates? The jawed vertebrates (gnathostomes) fall into two major taxa, the Chondrichthyes (cartilaginous fishes) and Osteichthyes (bony fishes). The latter taxon includes sarcopterygians (coelacanths, lungfishes, and tetrapods) and actinopterygians (ray-finned fishes). Are fishes jawed vertebrates? Gnathostomes or “jaw-mouths” are vertebrates that possess jaws. One of the most significant developments in