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

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$: All vertebrates are chordates but all chordates are not vertebrates.
Reason $(R)$: Notochord is replaced by vertebral column in the adult vertebrates.
In the light of the above statements,choose the most appropriate answer from the options given below:

Which of the following is true for $Salpa$?

"All vertebrates are chordates but all chordates are not vertebrates". Justify the statement.

Retrogressive metamorphosis is found in

Besides $Annelida$ and $Arthropoda$,metamerism is found in