Chapter_34_Vertebrate_Evolution_and_Diversity

Chapter_34_Vertebrate_Evolution_and_Diversity - BIOLOGY...

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CHORDATA 1. Notochord Longitudinal, flexible rod located between the digestive tube and the nerve cord. Later develops into a gelatinous material of disks between the backbones of most vertebrates. 2. Dorsal, Hollow Nerve Cord Developing from the plate of the ectoderm, the nerve cord rolls into a tube located dorsal to the notochord. It later develops into the brain and spinal cord. 3. Pharyngeal Slits Slits allow water to enter the mouth and exit without having to travel through the whole digestive system. Later develops for gas exchange and other functions for vertebrates such as hearing and jaw support. 4. Muscular, Postanal Tail A tail extending posterior to the anus, it contains skeleton that usually provides the propulsion force in aquatic vertebrates. Subphylum Urochordata -Examples: tunicates, sea squirts Commonly called tunicates, most are sessile animals, meaning they stick themselves to objects such as rocks, docks, or even boats. Others are free-swimming all their life. The larvae stage of tunicates shows all 4 chordate trademarks, with a single gene called Manx determining if a tail, notochord or dorsal nerve will develop. The only characteristic of an adult tunicate that suggests its resemblance of chordate is the pharyngeal slits, as it doesn’t have any trace of a notochord, a nerve cord or a tail. http://www.mun.ca/biology/scarr/Urochordata.html Subphylum Cephalochordata -Examples: lancelets http://www.vialattea.net/spaw/Image/biologia/lancelet.jpg Commonly known as lancelets, they have all four of the characteristics of a chordate in its adult stage Though feeble swimmers, they display a
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Chapter_34_Vertebrate_Evolution_and_Diversity - BIOLOGY...

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