Protochordates

Introduction: Protochordates can be defined as the primitive group from which chordate animals developed. Actually protochordates include all animals which were prior to the chordates.

Distinguishing characters of protochordates:  Following are t
he important characters of group Protochordata:
- They have a small rod like structure on the dorsal side of their body which is called notochord.
- They have the dorsal tubular nervous system whch is not very well- developed and is of primitive type.
- they have the primitive type of gill slits
Protochordate animals may have the notochord in the different places like in tail region or in head region and in one half region of the body.
Depending on the position of the notochord the group protochordata is again divided into following subphylum:
(1) Subphylum - hemichordata in which the notochord is present in the anterior one half of the body. The representative animal os this subphylum is called Balanoglossus.
(2) subphylum - urochordata in which the notochord is present in the tail region. The representative animal of this subphylum is called herdmania.
(3) Subphylum - cephalochordata. The representative animal of this phylum is called Amphioxus.
It is very important to know that all these three subphyla of the group protochordata although exhibit the primitive characters of phylum chordata can not be included under vertebrata because they do not have fdwell developed vertebral column. But they have the initial form of vertebral column which is just the notochord or the rod like structure found in the dorsal side of the body.