2005_campbl34a

2005_campbl34a - Chapter 34a: Vertebrates (sea squirts...

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Chapter 34a: Vertebrates (sea squirts through birds)
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Chordate Phylogeny
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Chordate Characteristics
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Subphylum Urochordata The urochordates include the tunicates, a.k.a., sea squirts The tunicates are mostly sessile, filter feeding animals that look almost nothing like a chordate However, their larval form possesses all of the basic characteristics of a chordate
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Tunicate: Urochordate
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Background: “ Pyura stolonifera is a solitary ascidian that occurs in bunches on the seafloor around the southern half of Australia. This bunch is in about 6 meters of water off Largs Bay, Adelaide.” Image to the left: This is a closeup of the same colony, the ascidians are generally covered with this light purple sponge.
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Tunicate Larva The notochord serves as a primitive internal support structure The notochord is a stiffened but still flexible rod found between the ventral (front/bottom) gut and the dorsal (back/top) nerve cord
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Subphylum Cephalochordata Cephalochordates, the lancelets, retain a chordate body plan throughout life In addition to the four defining chordate characteristics, lancelets, as well as tunicate larvae, have somites Somites are blocks of musculature arranged in segments along the bodies of lancelets and fishes (as well as derivations of this segmentation found in tetrapods)
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Lancelet: Cephalochordate Pharyngeal slits serve as filter- feeding devices in primitive chordates
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Class Myxini Class Myxini are represented in modern times by the hagfish, a.k.a., slime eels These are jawless invertebrate chordates Technically hagfish are not fish; they are more like “sophisticated” lancelets
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Hagfish, a Craniate Hagfish have cartilaginous skulls but no jaws and no vertebrae
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Notochord, Nerve Cord, Etc. In more modern forms, the notochord exists during development but is modified with development, e.g., into the gelatinous material of the intra-vertebral disks
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Primitive Chordates I have eyes and brain but no skull! I’ve got a skull, I am a craniate!
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Class Cephalaspidomorphi Class cephalaspidomorphi is represented in extant lineages by lampreys Lampreys lack jaws, like their non-vertebrate, chordate ancestors and hence are known as jawless fish Jawless fish were the vertebrate forerunners of the jawed fish Lampreys in addition lack paired fins
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2005_campbl34a - Chapter 34a: Vertebrates (sea squirts...

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