Apart from Annelida and Arthropoda,metamerism is also exhibited by ............ .

What is the location and function of the notochord?

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 $(R):$ The members of subphylum Vertebrata possess a notochord during the embryonic period; the notochord is replaced by a cartilaginous or bony vertebral column in adults.
In the light of the above statements,choose the correct answer from the options given below:

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

The following are the statements about non-chordates:
$A$. Pharynx is perforated by gill slits.
$B$. Notochord is absent.
$C$. Central nervous system is dorsal.
$D$. Heart is dorsal if present.
$E$. Post anal tail is absent.
Choose the most appropriate answer from the options given below:

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: