Chordata is a phylum of animals to which the vertebrates and a few related groups belong. Typically, the bilaterally symmetrical body is supported internally by a notochord or a vertebral column, running longitudinally through the segmental musculature, above the visceral cavity and below the tubular nerve cord. Specialized sensory organs for vision, olfaction, taste, hearing, and equilibrium are concentrated near the anterior end of the body adjacent to the brain and mouth. In aquatic chordates a series of gill slits are open from the pharnyx to the exterior. These admit a current of water to be strained of food particles by the gills, which also interchange oxygen for waste products in the blood stream. Gill slits also appear in the embryos of terrestrial classes. Haemoglobin is the active oxygen-carrying pigment of the blood, which is contained in a closed system of vessels, propelled by a muscular heart from which it flows anteriorly to the gill region, thence dorsally past the...
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References
Alexander, R. M., 1975. The Chordates. Cambridge: Cambridge Univ. Press, 480p.
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Gregory, J.T. (1979). Chordata . In: Paleontology. Encyclopedia of Earth Science. Springer, Berlin, Heidelberg. https://doi.org/10.1007/3-540-31078-9_33
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