Chordates

Chordates
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Characteristics of Chordates

• All chordates have a notochord, dorsal nerve cord, pharyngeal pouches, & postanal tail at some time in their life
• Notochord is a firm, flexible rod of tissue located on the dorsal side of the body that becomes part of the endoskeleton in vertebrates
• Dorsal nerve cord is a hollow tube lying dorsal to the notochord that becomes the brain & spinal cord in vertebrates
• Pharyngeal pouches are small outpockets of the anterior part of the digestive tract that become gills in aquatic chordates & jaws, inner ear, & tonsils in terrestrial chordates
• Postanal tail consists of muscle tissue & lies behind the posterior opening of the digestive tract

Subphyla of Chordates

• The Phylum Chordata  includes all of the vertebrates, as well as two groups of marine animals that lack backbones and are called invertebrate chordates
• The phylum is divided into three subphyla, determined by the development of the notochord
• Subphylum Cephalochordata contains about 24 species of blade-shaped animals known as lancelates that retain the notochord, dorsal nerve chord, pharyngeal pouches, and postanal tail throughout their life
• Subphylum Urochordata  contains 2,000 species commonly called tunicates because their bodies are covered by a tough covering, or tunic
  * Called sea squirts because they shoot out a stream of water when touched
  *Sessile, barrel-shaped, filter feeding animals that live on the sea bottom
  *Adults have a pouch-like pharynx with slits
  *Adults do not have a notochord, dorsal nerve cord, or postanal tail
• Subphylum Vertebrata is the largest subphylum in which the notochord is replaced with vertebrae
  *  Skeletons consist of bone &/or cartilage
  * Brain is protected by a cranium
  * Well developed 4 chambered heart with a closed circulatory system
  * Includes fish, amphibians, reptiles, birds, & mammals