Which of the following groups of characters is present in all chordates at some stage in their life?

Assertion: Notochord is a mesodermally derived rod-like structure formed on the dorsal side during embryonic development of chordates.
Reason: Notochord is replaced by the vertebral column in the adult vertebrate.

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 $Cephalochordata$.

The group $Amniota$ includes:

Which of the following is present during some stage of the life cycle in animals belonging to the phylum $Chordata$?

Which of the following organisms possess an endoskeleton?