$A$ rabbit shows resemblance with a frog in which of the following features?

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

In vertebrates,the notochord is replaced by which structure during the embryonic stage?

Echinoderms and chordates have

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 $Cephalochordata$.

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