Characteristics of the Phylum Chordata:

All members of the Phylum Chordata have the following characteristics, at least at some time during their development.

Notochord A firm, flexible rod of specialized cells that becomes the endoskeleton in vertebrates. Dorsal nerve cord A hollow tube above the notochord that becomes the spinal chord and brain in vertebrates: Pharyngeal pouches Out-pockets in the pharynx, the portion of the digestive tract between the mouth and the espohagus. Become gill chambers and gills in aquatic chordates. Become jaws, inner ear, and tonsils in terrestrial chordates. Post-anal tail A tail located posterior to the anal opening.

Phylum Chordata

• Subphylum Cephalochordata: contains about 24 species of blade-shaped animals known as lancelates.   They 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. They are also known as sea squirts  because they shoot out a stream of water when touched. Most tunicates are sessile, barrel-shaped, filter feeding animals that live on the sea bottom. Adult tunicates have a pouch-like pharynx with slits, but they do not have a notochord, dorsal nerve cord, or postanal tail. These chordate characteristics are lost during metamorphosis.

Characteristics of the Subphylum Vertebrata:

The phylum is named for the vertebrae.
Parts of the axial skeleton:
• Skull - bones protecting the brain.
• Backbone - bones protecting the nerve cord and supporting the body.
Parts of the appendicular skeleton:
• The pelvic and pectoral girdles attach to the axial skeleton.
• Front limbs attach to the pectoral girdle and hind limbs attach to the pelvic girdle.

Of the 7 classes of vertebrates, three are fish.

1 - Class Agnatha the jaw-less fish (lampreys and hagfish)

Class characteristics:

Eel-shaped body
Cartilage skeleton
Unpaired fins
Jawless mouth
 
 

2 - Class Chondrichthyes the cartilage fish (sharks, rays, and skates)

Class characteristics:

Cartilage skeleton
Placoid Scales