In the sub-phylum $\left(\mathrm{i}\right)$ notochord is present only in the larval tail, while in $\left(\mathrm{ii}\right)$, it extends from head to tail region and is persistent throughout their life. In $\left(\mathrm{iii}\right)$  class of vertebrata notochord is replaced by cartilaginous vertebral column and $\left(\mathrm{iv}\right)$class of vertebrata the notochord is replaced by bony vertebral column. Select the option which is correct for all $\left(\mathrm{i}\right) - \left(\mathrm{iv}\right)$blanks