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chordates
chordates Chordates are interesting to us because they include our own taxonomic group, the vertebrates. The phylum as a whole is characterized by the presence of a longitudinal cartilaginous stiffening rod (the notochord), a single tubular dorsal nerve cord, and perforations in the pharynx comparable to gill slits. On the basis of these and additional characters we divide the phylum into three subphyla. The urochordates or tunicates are sessile (attached to the bottom) marine filter-feeders, and rather sponge-like as adults. The larvae, however, are tadpole-shaped and mobile and, unlike the adults, show the full complement of chordate characters. The cephalochordates include only about twenty species of two genera of organisms commonly called amphioxus. They are small fish-like organisms (about 7 cm long) in which the chordate characters are retained in the adult. They live in sandy coastal sediments and filter the interstitial waters. The vertebrates are characterized by the presence of a bony skeleton and a brain. Although they retain the chordate characters as adults gill slits are present only in the embryonic stages of land vertebrates.
Study of types of cell division shows that chordates are most closely related to echinoderms, and it is currently accepted that echinoderms and lower chordates diverged from vertebrate ancestors no later than the Early Cambrian. Although fossil chordates (other than vertebrates) are rare, a fossil cephalochordate Pikaia is known from the Middle Cambrian Burgess Shale, and vertebrates have now been reported from the Middle Cambrian of Chengjiang, southern China. David K. Elliott |
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PAUL HANCOCK and BRIAN J. SKINNER. "chordates." The Oxford Companion to the Earth. 2000. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. PAUL HANCOCK and BRIAN J. SKINNER. "chordates." The Oxford Companion to the Earth. 2000. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O112-chordates.html PAUL HANCOCK and BRIAN J. SKINNER. "chordates." The Oxford Companion to the Earth. 2000. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O112-chordates.html |
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chordate
chor·date / ˈkôrdət; -ˌdāt/ • n. any animal of the phylum Chordata, including all vertebrates as well as the invertebrate sea squirts and lancelets, distinguished by the possession of a notochord at some stage during their development. • adj. of or related to the chordates. |
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"chordate." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "chordate." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O999-chordate.html "chordate." The Oxford Pocket Dictionary of Current English. 2009. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O999-chordate.html |
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chordate
chordate Any member of the Chordata, a large phylum of vertebrates and some marine invertebrates, which, at some stage, have rod-like, cartilaginous supporting structures (notochords). Invertebrate chordates are divided into three subphyla: tunicates (seasquirts); Cephalochordata (amphioxus); and Hemichordata (acorn worms).
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"chordate." World Encyclopedia. 2005. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "chordate." World Encyclopedia. 2005. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O142-chordate.html "chordate." World Encyclopedia. 2005. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O142-chordate.html |
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chordate
chordate
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•Margate • Irangate • tailgate
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•promulgate • elongate • toll gate
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•objurgate • expurgate • propagate
•arrogate • abrogate
•derogate, interrogate
•corrugate • subrogate • watergate
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"chordate." Oxford Dictionary of Rhymes. 2007. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>. "chordate." Oxford Dictionary of Rhymes. 2007. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O233-chordate.html "chordate." Oxford Dictionary of Rhymes. 2007. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O233-chordate.html |
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