(i) None chordata: Those animals which do not have notochord are called non-chordata. Protozoa, Metazoa, Porifera, Cnidaria, Platyhelminthes, Nematoda, Mollusca, Annelida, Arthropoda I Echinodermata are non-chordata. Such as Hydra (Hydra vulgaris), cockroach (Periplaneta americana), tapeworm (Taenia solium), snail (Pila globosa), sea star (Asterias rubens) etc.
(ii) Chordata: All animals which have notochord in their body are called Chordata. All animals in the order Chordata have notochords. Animals in the order Chordata are divided into three suborders.
• Urochordata: Urochordata only have a notochord in the tail region in the larval stage. E.g. Ascidia.
• Cephalochordata: In Cephalochordata the notochord extends from the apex of the head to the caudal region. Their notochord remains for life. For example, Branchiostoma.
• Vertebrata: In vertebrates the notochord is replaced by the spinal cord. E.g. Ascidia.