Branchiostoma belongs to

All vertebrates possess ......... .

Enterocoelous coelom is found in

Cephalochordates are ..........

Which one of the following features are true for chordates?
$(a)$ Heart is ventral.
$(b)$ Pharyngeal gill slits present.
$(c)$ Central nervous system is ventral,solid and single.
$(d)$ Post-anal tail is present.
$(e)$ Notochord is present.
Choose the most appropriate answer from the options given below:

The notochord is an organ derived from which embryonic layer?