All vertebrates are distinguished by a further developmental stage, in which they derive a fourth layer of basic tissue called “neural crest”. This makes a number of unique features in all vertebrates, including most of the front part of the head, and the cartilaginous bars that make up the skeleton supporting the gill slits (i.e, the pharyngeal arches). There are many, many other similarities between all vertebrates, including a trunk region in the embryo where the mesoderm is segmented on the top portion (somites) and unsegmented on the bottom portion (lateral plate). The various fates of the different portions of the portions of the mesoderm is the same in all vertebrates. E.g., the somites make the striated muscle, dermis of the skin, and the backbone. The lateral plate makes the smooth muscle of the gut, the heart muscle, and the limb bones.