Classification Of Phylum Chordata
Urochordata (tunicates) 
Cephalochordata (lancelets) 
Vertebrata (vertebrates) 
It is also known as Tunicate because the body of an adult is enclosed within
a tunic made up of cellulose -like substance known as tunicin.
Notochord can be seen only in the larval stage and disappears in the adults.
The nerve cord present in larva is replaced by a dorsal ganglion in adults.
The larva can move and undergoes a metamorphosis.
The atrium is present.
Motile adult and larval stage.
The tail is present throughout life.
They show progressive metamorphosis.
The notochord is found throughout life.
Numerous well-developed pharyngeal gill slits are present.
These are advanced chordates and have cranium around the brain.
The notochord is replaced by a vertebral column in adults.
This is why it is said that ‘all vertebrates are chordates but all chordates are not vertebrates’.
A high degree of cephalization is observed.
The epidermis is multi-layered.
They consist of three types of muscles-striped, unstriped and cardiac.
They have a well-developed coelom.
The alimentary canal is complete.
The heart is three or four-chambered.
They have well-developed respiratory and excretory systems.
Endocrine glands are present in all.
They are unisexual and reproduce sexually, hagfish being an exception.
Subphylum Vertebrata is further classified into seven classes. They are:
Cyclostomata 
Chondrichthyes 
Osteichthyes 
Amphibia 
Reptilia 
Aves 
Mammalia 