Phylum Chordata is an important phylum. Its name is derived from the notochord.
All the chordates possess three basic characters:
It is an important character of chordates. The notochord is present in all the chordates. It may be present in larval or embryonic stages or throughout life. The notochord is a semi-rigid rod-like structure. It is composed of vacuolated cells (cells containing large vacuoles like plant cells). These cells are filled with proteinaceous material.
Notochord mostly extends throughout the length of the body. It is present between the enteric canal (digestive canal) and the dorsal hollow central nervous system. Its primary function is to support the body. It acts as a skeletal axis and stiffens the body.
All the chordates have a central nervous system. It is hollow and dorsal in position.
All chordates develop paired gill slits or gill openings in their embryonic stages. These gill slits are non-functional in some chordates. In some chordates, these are functional during a small period of their life history e. g. frog. In other chordates, these are functional throughout their life, e.g. Amphioxus and fishes.
Chordates are divided into two major groups:
In these animals, the braincase or skull is absent. Notochord remains intact throughout life. These are also called lower chordates e.g. Amphioxus. Acrania has two sub-phyla, Urochordata and Cephalochordate.
In these animals, a braincase or skull is present. These are called higher chordates. The notochord is replaced by the vertebral column. So they are also called vertebrates. Craniata has a single subphylum, Vertebrata.
Example: Molgula.
Notochord and nerve cord extends along the entire length of the body. Notochord persists throughout life e.g. Amphioxus.
The brain of these animals is enclosed in a braincase or cranium. They have a vertebral column. Chordates are commonly divided into two superclasses:
Vertebrates may be divided into two groups on the basis or absence of embryonic or fetal membrane called the amnion.
This phylum has a combination of both invertebrate (Echinoderm) and chordate characteristics. Hemichordata, Echinodermata, and Chordata form a branch of the animal kingdom called Deutrostome. As they have a close relationship with the chordates, so they are called chordates. The common examples of this phylum are Blanoglossus and Saccoglossus.
Other Related Phyla:
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