What is a Notochord?
A notochord is the defining characteristic of members of the phylum Chordata, a large and diverse biological group which includes all animals with spines, or backbones, along with more primitive chordates. The notochord has very large cells which are densely arranged within a protective sheath. Chordates are divided into three subphyla, depending on what form their notochords take and when they appear. At any developmental stage, a notochord acts as a form of support for the animal that possesses it, giving animals the ability to do things such as walking upright. The most primitive group of chordates, urochordates, also called tunicates, only have a notochord in the larval stages of development. The animals in this group are pelagic, meaning that they are found in the world’s oceans, and there are a number of representative species, most of whom are only known to biologists. These animals do provide an insight into the development of chordates, however, showing the notochord at an ear