This phylum derives its name from one of the common characteristics of this group namely the notochord (Gr. noton, back + L. chorda, cord). The animals belonging to all other phyla of the Animal Kingdom are often termed ‘the non -chordates’ or ‘the invertebrates’ since they have neither notochord nor backbone in their body. The backboned animals (vertebrates), together with a few closely re-lated animals which do not possess a backbone, are included in this phylum. Most of the living chordates are familiar vertebrate animals.
The Phylum Chordata is classified into four sub phyla:
Sub phylum 1. Hemichordata,
Sub phylum 2. Cephalochordata
Sub phylum 3. Urochordata
Sub phylum 4. Vertebrata.
First three sub phyla are collectively known as Protochordates. Since the members of these sub phyla do not have a cranium or skull they are also referred to as Acrania
Ventral heart: The heart is chambered. It is located ventral to the alimentary canal.
Closed blood vascular system: In chordates, the blood passes through a continuous system of tubes namely arteries, capillaries and veins.
Hepatic portal system: In chordates, the food laden blood from the digestive tract passes through the capillary net work in the liver, before reaching the heart. Thus the veins originating from the digestive tract as capillaries and ending in the liver again as capillaries constitute the hepatic portal system.
