Phylum Chordata

Phylum Chordata

This phylum derives its name from one of the common characteristics of this group namely the notochord (Gr. Noton – back L. chorda - cord). The animals belonging to all other phyla of the Animal Kingdom are o en termed ‘as non -chordates’ or ‘invertebrates’ since they neither have notochord nor backbone in their body. The animals with backbones are chordates. Chordates are of primary interest because human beings are members of this group.

1. Sub-phylum Acraniata – Prochordata

The Prochordates are considered as the forerunner of vertebrata. Since they do not have a cranium or skull they are referred to as Acrania. The classification of the Prochordates is based on the nature of the notochord. The Phylum Prochordata is classified into three sub phyla namely Hemichordata, Cephalochordata and Urochordata.

2. Sub phylum Hemichordata

Hemichordates are marine organisms without backbone. They mostly remain as tubiculous forms. The body is so , vermiform, unsegmented, bilaterally symmetrical and triploblastic. The notochord is persistent as the stomochord in the anterior region of the animal. Eg. Balanoglossus (Acon worms)

3. Sub phylum Cephalochordata

Cephalochordates are small sh like marine chordates with unpaired dorsal ns. The persistent notochord extends forward beyond the brain. Eg. Amphioxus.

4. Sub phylum Urochordata

In Urochordata the notochord is con ned to the tail region of the larva. The adults are mostly degenerate, and are sessile forms. The body is enveloped by a tunic or test. Eg. Asicidian