ZOOLOGY STUDY GUIDE - Ye. O. Nevedomska - 2013

LECTURE 13. GENERAL CHARACTERISTICS OF THE PHYLUM CHORDATA (Chordata)

1. General Characteristics of the Phylum Chordata

Chordates are a phylum of animals characterized by an Axial Skeleton in the form of a notochord located above the digestive tube; the dorsal nerve cord is positioned above the notochord. The notochord (from Greek chorde — string) is an elastic, unsegmented skeletal axis in chordate animals.

There are approximately 51,000 known extant species of the phylum Chordata. Chordates inhabit land, oceans, seas, and freshwater bodies.

General characteristics:

1. In the Cytology/cytology/16.html">Early stages of chordate development, i.e., in embryos (in higher chordates: fish, amphibians, reptiles, birds, mammals) or throughout life (in lower chordates: lancelets, cyclostomes), the support for the entire body is the internal axial skeleton, or notochord.

2. Chordates are triploblastic organisms with bilateral Symmetry.

3. They possess a secondary body cavity — a coelom, which contains the internal Organ Systems.

4. The digestive tube is located beneath the notochord.

5. Pharyngeal slits are present in the Pharynx; these are rows of paired openings in the pharynx that open to the outside either directly or through the peribranchial cavity. In primary aquatic animals (lancelets, cyclostomes), pharyngeal slits persist throughout life. In other animals (amphibians, crocodiles, dolphins, whales, seals) that transitioned to terrestrial life or returned to an aquatic environment (secondary aquatic animals), pharyngeal slits form as rudiments during embryonic development but are replaced by Lungs before birth.

6. The tubular Central Nervous system is located above the notochord.

The Classification of the phylum Chordata is presented in Diagram 9.

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Diagram 9. Classification of the phylum Chordata.