Phylum Chordata is the most advanced animal phylum.
Chordata are animals which possess a notochord at any stage of their life .They are most adaptable, most successful and most widely distributed animals showing diversity of form, habits and habitats.
1. All chordates are bilaterally symmetrical
2. They are true metamerically segmented animals.
3. They are triploblastic animals having organ system grade of body organizations.
4. Post anal tails are usually present in chordates
5. They are true coelomate animals
6. Notochord is present at some stages or replaced by back bone or ring like vertebrae forming the vertebral column.
7. Gill clefts are present at some stages of life.
8. Alimentary canal is placed always ventral to the nerve cord.
9. Anus is well differentiated and opens before the last segment.
10. Heart is placed ventrally, blood flows towards the posterior direction in dorsal blood vessel.
11. Hemoglobin, a respirator pigment is present in red blood corpuscles
12. Hepatic portal system is present in chordates
13. Respiration is either by gills or by lungs.
14. Nervous system is hollow; brain is located dorsal to the pharynx in the head.
15. Nerve cord is single, dorsal, and hollow without ganglia.
16. Dorsal and ventral nerve roots are separate.
17. Mostly sexual reproduction occurs in chordates
18. They are cold blooded as well as warm blooded animals.
Phylum Chordata is divided into three subphyla, subphylum Urochordata or Tunicata, subphylum Cephalochordata or Acrania and subphylum vertebrata. The first two subphyla are considered primitive and often referred to as protochordates or non-vertebrate chordates. All of them are marine and possess notochord but never form vertebral column.