Why urochordata and cephalochordata is referred to as protochordates?

Dear student,
Phylum chordata of animal kingdom is divided into 2 sub-groups protochordata/acraniata(without brain box or cranium) and euchordata/craniata( cranium is present).
Again protochordata is divided into two sub-phylum urochordata/tunicata (notochord is present only in larval tail, eg. Salpa,doliolum) and cephalochordata (notochord extends from head to tail region, eg. Branchiostoma)

Urochordata and cephalochordata which are acraniates are considered as primitive and often referred to as protochordates or non-vertebrate chordates.

Protochordata/Acraniata/Non vertebrate chordates is a sub group under chordata which involves chordates without cranium or brain box.

Their basic features include:
  • Presence of notochord
  • Central nervous system is dorsal,hollow and single
  • Pharynx perforated by Gill slits
  • Heart is ventral
  • A post anal tail is present
  • Gut is ventral to nerve chord.
  • Absence of cranium or brain box.
Due to the presence of these features urochordata and cephalochordata is referred to as protochordates


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