Following characters are used to classify the phylum Chordata –
1. Skull – Presence of skull (Craniata) or absence of skull (Acraniata)
2. Jaws – Absence of jaws (Agnatha) or presence of jaws (Gnathostomata)
3. Locomotion – Locomotion by paired fins (Pisces) or locomotion by paired legs (Tetrapoda)
4. Extra – embryonic membranes – Absent (Anamniota) or Present (Amniota)