The body is divided into head and trunk in:

Which of the following statements are true for the phylum $Chordata$?
$(a)$ In $Urochordata$,the notochord extends from head to tail and is present throughout their life.
$(b)$ In $Vertebrata$,the notochord is present during the embryonic period only.
$(c)$ The central nervous system is dorsal and hollow.
$(d)$ $Chordata$ is divided into $3$ subphyla: $Hemichordata$,$Tunicata$,and $Cephalochordata$.

In chordates,the brain is formed from which of the following structures?

In some chordates,the notochord is replaced by the vertebral column. Such animals are called vertebrates. Which one of the following statements is correct?

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

Which of the following is not a subphylum of Chordata?