Which of the following statements is true?

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:

$A$ rabbit shows resemblance with a frog in which of the following features?

Give a scientific reason: Annelids are considered evolutionary precursors of molluscs.

Assertion : Acraniata is a group of organisms which do not have a distinct cranium.
Reason : It includes small marine forms without a head.

Which of the following phyla possess a post-anal tail at some stage of their life?