Protochordata (Acrania)

Protochordata (Acrania) The protochoradates are considered as the fore runners of vertebrata The classification of the protochordates is based on the nature of the noto- chord.

Sub phylum : Hemichordata .These are exclusively marine organisms. They are solitary or colonial forms. They mostly remain as tubiculous forms. The body is soft, vermiform, unsegmented,bilaterally symmetrical and triploblastic. The body is divisible into three distinct regions namely proboscis, collar and trunk. The body wall is composed of single layer of epidermal cells. The dermis is absent. They have no endoskeleton. A projection from pharynx, projecting inside the proboscis  may be considered as notochord. They have a spacious coelom lined by coelomic epithelium. The alimentary canal is a straight tube running between mouth and anus. They are ciliary feeders. Sexes are separate. Examples :  Balanoglossus ,  Saccoglossus .

Protochordata (Acrania)

The protochoradates are considered as the fore runners of vertebrata

The classification of the protochordates is based on the nature of the noto- chord.

Sub phylum : Hemichordata . These are exclusively marine organisms. They are solitary or colonial forms. They mostly remain as tubiculous forms. The body is soft, vermiform, unsegmented,bilaterally symmetrical and triploblastic. The body is divisible into three distinct regions namely proboscis, collar and trunk. The body wall is composed of single layer of epidermal cells. The dermis is absent. They have no endoskeleton. A projection from pharynx, projecting inside the proboscis  may be considered as notochord. They have a spacious coelom lined by coelomic epithelium. The alimentary canal is a straight tube running between mouth and anus. They are ciliary feeders. Sexes are separate.

Examples : Balanoglossus , Saccoglossus .

Sub phylum : Cephalochordata .

Cephalochordates are small fish like marine chordates. The persistent notochord extends forward beyond the brain . Hence these are called cephalochordates. The epidermis is single layered. Paired fins are absent. Muscles, nephridia and gonads are segmentally arranged. The pharynx is large with numerous gills. It is a filter feeder. Example :  Amphioxus.