In: Biology
Answer: Tunicata are the special type of organism which have its adult stage less advanced then its larval stage. Urochordata or Tunicata is the organism which have notochord in its larval stage. The notochord is present in the tail region (Uro= tail).only. As the organism develop means at the time of metamorphosis this notochord is lost. So the chordata character(that is presence of notochord) is lost during adult stage.Only they have pharangial gill clift at adult stage as character of chordata. So we can say that the absence of notochord is the feature which is responsible for non cephalization in Tunicates. For the process of Cephalization their must be the attachment of spinal cord, brain with the various nerves(generally with CNS) for the quick movements and response. As we know that notochord play a crucial role in development of nervous system so by the absence of this in adult stage no cephalization is possible.