Which marine animals possess a notochord only during their larval stage?

The notochord is restricted to the tail region only in:

Observe the following simplified scheme of the division $Vertebrata$ and choose the correct option that matches with the letters given in the boxes.
$Vertebrata$ (Division)
- $p$ (Lacks jaw)
- $q$ (Bears jaw)
- Super class
- $r$ (Bear fins)
- $s$ (Bear limbs)

In $Urochordata$,the notochord is found in:

Post-anal tail is present in

Which of the following statements are true for the phylum $Chordata$?
$(a)$ In $Urochordata$,the notochord extends from head to tail and is present throughout their life.
$(b)$ In $Vertebrata$,the notochord is present during the embryonic period only.
$(c)$ The central nervous system is dorsal and hollow.
$(d)$ $Chordata$ is divided into $3$ subphyla: $Hemichordata$,$Tunicata$,and $Cephalochordata$.