All vertebrates, without any exception, are characterised by the presence of

The sub-phylum Vertebrata (or Craniata) have a well-developed nervous system that is differentiated into brain and spinal cord. Brain is protected by a brain box called cranium, so that are also called as craniates. Scales and jaws are absent in cyclostomes. Limbs are absent in fishes, snakes and some amphibians (e.g., Ichthyophis).