notochord

Examples of notochord in the following topics:

• Characteristics of Chordata

  • Animals in the phylum Chordata share four key features: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.
  • In some chordates, the notochord acts as the primary axial support of the body throughout the animal's lifetime.
  • The notochord, however, is replaced by the vertebral column (spine) in most adult vertebrates.
  • In chordates, it is located dorsally (at the top of the animal) to the notochord.
  • In chordates, four common features appear at some point during development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.

• Phylum Chordata

  • The phylum Chordata contains all animals that have a dorsal notochord at some stage of development; in most cases, this is the backbone.
  • A notochord, or a longitudinal, flexible rod between the digestive tube and the nerve cord .
  • A dorsal nerve cord which develops from a plate of ectoderm that rolls into a tube located dorsal to the notochord.
  • For example, tunicate larvae have both a notochord and a nerve cord which are lost in adulthood .
  • All chordates possess a notochord, or a type of flexible support rod, at some point in their development.

• Chordates and the Evolution of Vertebrates

  • Adults only maintain pharyngeal slits and lack a notochord, a dorsal hollow nerve cord, and a post-anal tail.
  • Members of Cephalochordata possess a notochord, dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail in the adult stage.
  • They do not have a true brain, but the notochord extends into the head, which gives the subphylum its name ( "cephalo" is Greek for head).
  • (c) In the adult stage, the notochord, nerve cord, and tail disappear.
  • Adult lancelets retain the four key features of chordates: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.

• Bilaminar Embryonic Disc Development

  • As gastrulation progresses, the embryonic disc becomes trilaminar and the notochord is formed.
  • Through the through the process of neurulation, the notochord induces the formation of the notochord in the embryonic disc.

• Neurulation

  • Following gastrulation, the neurulation process develops the neural tube in the ectoderm, above the notochord of the mesoderm.
  • After gastrulation, the notochord—a flexible, rod-shaped body that runs along the back of the embryo—is formed from the mesoderm.
  • During the third week of gestation the notochord sends signals to the overlying ectoderm, inducing it to become neuroectoderm.

• Agnathans: Jawless Fishes

  • The skeleton of a hagfish is composed of cartilage, which includes a cartilaginous notochord that runs the length of the body.
  • This notochord provides support to the hagfish's body.
  • Unlike true vertebrates, hagfishes do not replace the notochord with a vertebral column during development.
  • Their notochord is surrounded by a cartilaginous structure called an arcualia, which may resemble an evolutionarily-early form of the vertebral column.

• Characteristics of Vertebrates

  • However, the subphylum Vertebrata is distinguished from the phylum Chordata by the development of the notochord into a bony backbone.
  • In vertebrates, the notochord develops into the vertebral column or spine: a series of bony vertebrae each separated by mobile discs .
  • However, a few vertebrates have secondarily lost their vertebrae and, instead, retain the notochord into adulthood (e.g., the sturgeon fish).
  • In chordates, the central nervous system is based on a hollow nerve tube that runs dorsal to the notochord along the length of the animal.
  • All chordates are deuterostomes, possessing a notochord.

• Vertebrate Axis Formation

  • They found that the transplanted embryo now had two notochords: one at the dorsal site from the original cells and another at the transplanted site.
  • This suggested that the dorsal cells were genetically programmed to form the notochord and define the dorsal-ventral axis.

• Establishing Body Axes during Development

  • They found that the transplanted embryo now had two notochords: one at the dorsal site from the original cells and another at the transplanted site.
  • This suggested that the dorsal cells were genetically programmed to form the notochord and define the axis.
  • These cell types are specified by the secretion of Shh from the notochord (located ventrally to the neural tube), and later from the floor plate cells.

• The Evolution of Craniata and Vertebrata

  • In adult vertebrates, the vertebral column replaces the embryonic notochord.