The most primitive members of this group are sea squirts, whose motile larval stage sports a muscular post-anal tail.  In craniates, the nervous system develop into a brain and head, while pharyngeal slits become gills, such as those in hagfishes, which technically are not true fish.  True fishes have jaws while lampreys do not, but since they both belong to the subphylum (*) vertebrates, they have an extensive skeletal system, including a spinal
The most primitive members of this group are sea squirts, whose motile larval stage sports a muscular post-anal tail.  In craniates, the nervous system develop into a brain and head, while pharyngeal slits become gills, such as those in hagfishes, which technically are not true fish.  True fishes have jaws while lampreys do not, but since they both belong to the subphylum (*) vertebrates, they have an extensive skeletal system, including a spinal column evolved from the shared notochord. FTP – name this phylum in the Animal Kingdom to which amphibians, reptiles, and mammals all belong.
The most primitive members of this group are sea squirts, whose motile larval stage sports a muscular post-anal tail.  
{Chordates} or {Chordata}