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
