Describe the characteristic features of different Prochordates with suitable diagrams.

Prochordates:

i. Prochordates are considered as the development of vertebrata.

As they do not have brain, hence they are referred as Acrania.

ii. These are divided into three sub-pylums which are Hemichordata, Cephalochordata and Urochordata.

iii. The three sub-phylums are classified on the basis of notochord.

Hemichordata

i. These are marine organisms.

ii. They do not have backbones.

iii. The body is soft, bilateral symmetrical and unsegmented.

iv. The notochord is persistent as the stomochord in the anterior region of the animal.

Balanoglossus

Cephalochordata

i. These are small fish.

ii. These are marine organisms with unpaired dorsal fin.

iii. The persistent notochord extends forward beyond the brain.

Amphioxus

Urochordata

i. The adults are mostly degenerate, and are sessile forms.

ii. The body is enveloped by a tunic or test.

iii. In Urochordata the notochord is confined to the tail region of the larva.

Ascidian