The phylum chordata is divided into different sub phyla. These are known as the urochordata, cephalochordate and vertebrata. They all have different features and they are described below.
The urochordata is also known as the tail notochord. They are also known as tunicata, as their body is enclosed in a tunic which is composed of the cellulose. In this case the notochord is present in the embryo stage. It disappears in the adult stage. It occurs in the tail portion. The larva also contains a dorsal nerve cord. However, in the adult it is replaced by a dorsal ganglion. There are numerous apertures in the pharynx known as stigmata. They are formed by the division of gill slits. The stigmata have an opening in the ectoderm referred as atrium. The larva undergoes certain changes known as metamorphosis. It is of retrogressive type which means the larva changes from better developed to less develop. The cephalochordate is also known as the head notochord. In these organisms the notochord extends till the anterior part of body. In this case the notochord is present throughout the life. It is also present in the adult stage. There are numerous apertures in the pharynx known as stigmata which are better developed than the urochordata. The stigmata have an opening in the ectoderm referred as atrium. The tail is also present throughout their life. Amphioxus is also known as lancelet as their both the ends are pointed.
The subphyla mentioned above are without the cranium. These are known as acrania. They are also referred as the primitive chordates.