What is the location and function of the nerve cord in chordates?

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:

Which of the following is $NOT$ included in Protochordata?

$A:$ Amphioxus is not a vertebrate.
$R:$ Amphioxus is not a chordate.

What is the classification of the subphylum $Vertebrata$?

Which of the following is $NOT$ found in invertebrates?