Which of the following is a distinct character of the phylum Chordata?

Assertion $(A)$: $Ascidia$ and $Salpa$ are placed under sub-phylum $Urochordata$.
Reason $(R)$: In $Ascidia$ and $Salpa$,notochord is present only in larval tail.
In the light of the above statements,choose the most appropriate answer from the options given below:

Statement-$1$ : Cephalochordata bears notochord all along the body throughout life.
Statement-$2$ : Urochordate bears vertebral column only in tail region throughout the life.
Then which is correct?

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)

Assertion: Notochord is a mesodermally derived rod-like structure formed on the dorsal side during embryonic development of chordates.
Reason: Notochord is replaced by the vertebral column in the adult vertebrate.

In which of the following animals is a post-anal tail found?