Non-chordates have:

There has been an increase in the number of chambers in the heart during the evolution of vertebrates. Name the classes of vertebrates that have two,three,and four-chambered hearts.

The most important distinctive character of $Chordata$ is the presence of

To which group does $Salpa$ belong?

In which of the following,the notochord is replaced by a vertebral column in the adult stage?

Assertion $A$: $Amphioxus$ is not a vertebrate.
Reason $R$: $Amphioxus$ is not a chordate.
Which option is correct for Assertion $A$ and Reason $R$?