Animals V: Chordates

Characteristics of Phyla Chordata
Most Chordates undergo neurulation,  have a  notochord,  a hollow  dorsal nerve cord,  pharyngeal slits, an  endostyle, and a post-anal tail  for at least some part of their life cycles.

Notochord: rod of connecting tissue (mesoderm) that forms in the embryo during gastrulation and guides the development of the vertebral column in vertebrates. In most verterbrate chordates the notochord's only remnants are the cartilaginous discs between each vertebrae.

Neurulation: The presence of a notochord induces neurulation by using growth factors to signal the ectoderm layer to form a neural plate. During primary neurulation, the neural plate then folds in on itself (as seen to the right) to form what eventually will become the dorsal hollow nerve tube. In vertebrates the anterior region of the dorsal hollow nerve tube expands to become a brain.

See also: Development &amp; Tissues

Chicken Embryo Development
Labeled chicken embryos (slides)

Labeled chicken embryo (actual)

Vertebrate Chordate Classes
Subphylum: Vertebrata (Craniata)
 * Agnatha: jawless fishes
 * Chondrichthyes: cartilaginous fishes
 * Osteichthyes: bony fishes
 * Amphibia 
 * Reptilia 
 *  Aves: birds
 * Mammalia

Invertebrate Chordate Classes
Subphylum: Protochordata
 * Urochordata: tunicates (seasquirts)
 * Larvacea: 


 * Cephalochordata: lancelets