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Phylum Chordata Animals

Main and the last phylum in the classification of animal kingdom is chordata. This phylum includes animals of great anatomical and physiological difference. This phylum includes the primitive chordates in protochordate (or acraniata) and evolved chordata in vertebrata (or craniata). Generally chordates are free living and non- chordate is totally or strictly a parasite. About 65,000 species are known living chordates.

Balfour (1880) was the first taxonomist who gave this name chordata. This is a Greek word-chorde means a chord and means bearing. It bears anotochord or dorsal chord essentially which is present in any stage of life.

Phylum Chordata Animals General Characters: These characters may be divided into-

1. Fundamental chordate characters.

2. Common characters of chordates and non-chordates.

3. Advance chordate characters.

Fundamental chordate characters:

These characters are present in any stage of life history essentially. There are three unique morphological characters-

(i) Notochord or chorda dorsalislit is an elastic skeletal rod present dorsally below the nerve cord and above the alimentary canal. It is present lengthwise from anterior to the posterior end of the body. In craniate or vertebrate adults this notochord is modified into the body of vertebrae or it forms a main part of the vertebral column not the whole vertebral column.

(ii) Dorsal tubular nerve cord-It is hollow, dorsal, fluid filled tubular structure develops from dorsal ectodermal infolding. It is present just above the notochord running from one end to another. It persists throughout the life but in few it degenerates before maturity.

(iii) Pharyngeal gill slits-These are the paired opening present in the pharynx and open outside. These are the out pushing of endodermal lining of pharynx. These gill clefts are present in any stage of life history of every chordate but in many lower vertebrates these are provided with lamellae which function as respiratory organs.' These structures are true gills.

Common characters of chordates and non-chordates

(i) Axiation-Presence of cephalic end and a tail with antero¬posterior axis.

(ii) Bilateral symmetry-The left and right halves are mirror images. (iii) Triploblastic condition-Three layers-outer ectoderm, middle mesoderm and inner endoderm.

(iv) Coelom-True coelomates lined entirely by mesoderm. In lower chordates the development of coelom is enterocoelic type but in higher chordates it is schizocoelic type.

(v) Metamerism-Similar and regularly repeated body segments are known as metameres (segments or somites), thus such animals are known as metamerically segmented animals.

Advance chordate characters:

(i) Living endoskeleton-Except few echinoderms the chordates are provided with living endoskeleton. Living endoskeleton helps in growth indefinitely and freely.

(ii) Efficient respiration-Higher chordates are provided with efficient respiratory organs¬lungs and tracheal path.

(iii) Ventral heart-Muscular heart placed ventrally and lies enclosed in the pericardial cavity filled with pericardial fluid and covered by pericardium.

(iv) Hepatic portal system-Food laden blood from the digestive tract is conveyed through a hepatic portal vein. This vein ramifies in liver, thus instead of pouring its blood in the heart, it is supplying to the liver.

(v) RBC or Erythrocytes- Containing haemoglobin a respiratory pigment.

(vi) Post anal tail-The posterior prolongation of vertebral column beyond the anus is a segmented tail. It is without coelom and without any visceral organ.

(vii) Centralization of nervous system:

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