Chordata

• Chorde: a string on rod
• ata: bearing

Chordata is bilaterally symmetrical, triploblastic, coelomates having a supporting skeletal rod i.e. notochord, a nerve chord, pharyngeal gill slits which may persist change or disappear in the adult. Phylum Chordata was created by Belfaur.

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Diagnostic characteristics of phylum Chordata

Presence of notochord

The notochord is an elastic solid, skeletal rod lies above the alimentary canal and below dorsal tubular nerve chord. It serves as the primitive internal skeleton.

Dorsal tubular nerve chord

It is the hollow fluid-filled tubular structure formed by infolding of ectoderm, lies above notochord and exterior to coelom.

Pharyngeal gill slits

These are paired gill slits which arise from the pharynx to exterior.

Beside these, ventral heart, close circulation, RBC, post-anal tail hepatic portal system etc are very important features of chordates. On the basis of position of notochord, phylum Chordata is divided into 4 subphylum;

• Hemichordata: Notochord at heart only. Eg;Balangle
• Urochordata: Notochord at tail only. Eg; Hardmania
• Cephalochordata: Notochord extends from head to tail. Eg; Branchiostoma
• Vertebrata or Craniata: Notochord is found in the embryonic stage and replaced by the vertebral column in the adult. Brain encloses within the cranium.