Though it is a defining feature of the phylum Chordata, most chordates do not retain this structure into adulthood, though tunicates and lancelets notably do.
When cells of this structure do not fully develop, lesions called Tornwaldt's cysts can form. During embryonic development, this structure produces a morphogen important in organ differentiation named after Sonic the Hedgehog. It is composed of a glycoprotein core surrounded by two collagen helices, and it served as a backbone in Haikouichthys. Though it is a defining feature of the phylum Chordata, most chordates do not retain this structure into adulthood, though tunicates and lancelets notably do. Identify this structure that is the precursor to the intevertebral disk, a structure found in the embryos of all chordates.
When cells of this structure do not fully develop, lesions called Tornwaldt's cysts can form.
{notochord} [do not accept or prompt on “dorsal nerve chord”]