Which of the following animals has a closed circulatory system?

$A$: All chordates have kidneys as excretory organs.
$R$: Kidneys help in the removal of metabolic wastes along with regulating the osmolarity of body fluids.

Which of the following animals is known as an invertebrate chordate?

Which one feature is common to $Amphioxus$,frog,sea horse,and crocodile?

Identify the correct statement regarding 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 $(R)$: 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: