part_of part of part of only in taxon develops from existence starts during Eumetazoa Chordata organ embryo stage multi-tissue structure neural tube digestive tract notochord http://upload.wikimedia.org/wikipedia/commons/6/64/Gray19_with_color.png The notochord appears early in embryogeny and plays an important role in promoting or organizing the embryonic development of nearby structures. In most adult chordates the notochord disappears or becomes highly modified. In some non-vertebrate chordates and fishes the notochord persists as a laterally flexible but incompressible skeletal rod that prevents telescopic collapse of the body during swimming[TOLWEB] notochordal In between vertebra the notochord becomes the nucleus pulposus, under it degenerates, and at anterior end in some species its tissue merges with some of the cranial bones.. Some organisms retain a post-embryonic notochord. mesoderm-derived structure ectoderm-derived structure chordamesoderm notochordal plate axial skeletal system