Usually,chordates have red blood containing red blood corpuscles. The blood is red due to the presence of the following pigment:

Which of the following is $NOT$ an exoskeleton of vertebrates?

$Branchiostoma$ is an example of

In $Urochordata$,the notochord is found in:

What do $a$ and $b$ represent in the given chart respectively?

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: