Biology

Phylum Chordata Characteristics & Classification

The Chordates

Chordata is an important phylum. Its name is derived from the notochord.Phylum Chordata diagram Endoskeleton is the chief basic character of the Chordata phylum. This endoskeleton is an important factor in the development and specialization of the higher animals. Man is the most important chordate. The chordates show a great variety. They live in all kinds of habitat.

Characteristics of Phylum Chordata

All the chordates possess three basic characters:Characteristics of Phylum Chordata

1. Presence of notochord

It is an important character of chordates. Notochord is present in all the chordate. 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.

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Notochord mostly extends throughout the length of the body. It is present between enteric canal (digestive canal) and the dorsal hollow central nervous system. Its primary function is to support the body. It acts as skeletal axis and stiffens the body.

2.      Hollow Dorsal Central Nervous System

All the chordates have central nervous system. It is hollow and dorsal in position.

3.      Presence of Gill Slits

All chordates develop paired gill slits or gill openings in their embryonic stages. These gill slits are non-functional in some chordate. In some chordates, these are functional during small period of their life history e. g. frog. In other chordates, these are functional throughout their life, e.g. Amphioxus and fishes.

Classification of Chordates

Chordates are divided into two major groups:

  • Acrania (protochordata)

In these animals, brain case 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.

  • Craniate (Vertebrata)

In these animals, brain case or skull is present. These are called higher chordate. Notochord is replaced by vertebral column. So they are also called vertebrates. Craniata has single subphylum, Vertebrata.

Protochordata (Acrania)

(Sub-phylum Urochordata)

  1. Notochord and nerve chord are present only in free swimming larva. These are absent in adults.
  2. Adult animals are sessile (cannot move).
  3. Their body is enclosed in a covering called tunic. So they are also called tunicate.

Example: Molgula.

(Sub-phylum Cephalochordata)

Notochord and nerve cord extend along the entire length of the body. Notochord persist throughout life e.g. Ampioxus.

Craniata

(Sub-phylum Vertebrata)

The brain of these animals is enclosed in brain case or cranium. They have vertebral column. Chordates are commonly divided into two super classes:

  • Pisces (fish): They are all strictly aquatic animals. It includes all types of fishes.
  • Tetrapoda: They are four footed animals. It includes class amphibian, reptilia, aves and mammalia.

Vertebrates may be divided into two groups on the basis or absence of embryonic or foetal membrane called amnion.

  • Anamniota: Foetal membrane or amnion is absent in these animal. It includes Cyclostomata, Chondrichthyes, Osteichythes and Amphibia.
  • Amniota: Foetal membrane or amnion is present in these animals. It includes Reptilia, Aves and Mammalia.

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Phylum Hemichordata

This phylum has a combination of both invertebrate (Echinoderm) and chordate characteristics. Hemichordata, Echinodermata and Chordata form a branch of animal kingdom called Deutrostome. As they have close relationship with the chordates, so they are called prechordates. The common examples of this phylum are Blanoglossus and Saccoglossus.

General Characteristics of Phylum Hemichordata

  1. Their bodies are soft and worm like.
  2. Body is divided into anterior proboscis collar and trunk (main body).
  3. Body wall is made up of unicellular epidermis. This epidermis contains mucous secreting cells.
  4. Digestive tube is straight. It may show variations.
  5. Coelomic cavities are also divided in to three regions of body in proboscis, collar and coelomic pouches.
  6. Circulatory system consists of a median dorsal and a median vessel.
  7. Respiratory system is composed of gill-slits. These gill slits form a dorsal row behind the collar.
  8. Excretory system is composed of single glomerulus. This glomerulus is connected to blood vessels.
  9. Nervous system has a sub-epidermal plexus of cells and fibers.

Other Related Phylums:

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