Then, one of those early deuterostomes became the very first chordate by gaining a notochord.

Over time, the chordate body plan gradually changed.

The larva of the invertebrate chordate Ciona intestinalis possesses only 36 striated muscle cells and lacks body segmentation.

In other words, we are vertebrates, which are a form of chordate, which are themselves a form of deuterostome.

Here we review the gene repertoire of Fads and Elovl in chordate genomes and the diversity of substrate specificities acquired during evolution.