CH 24 - Chapter 24 Animal Diversity II Vertebrates 24.1...

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Chapter 24 Animal Diversity II: Vertebrates
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24.1 What Are the Key Features of Chordates? All chordates have four distinctive structures 1. A notochord : a stiff flexible rod extending the length of the body 2. A dorsal, hollow nerve cord : lies above the digestive tract and expands anteriorly to form the brain 3. Pharyngeal gill slits : located in the pharynx that may form respiratory organs or may appear as grooves 4. A post-anal tail : the chordate tail extends past the anus
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Vertebrates Craniates Tetrapods Urochordata (tunicates) Cephalochordata (lancelets) Chondrichthyes (sharks, rays) Myxini (hagfishes) Actinistia (coelacanths) Actinopterygii (ray-finned fish) Petromyzontiformes (lampreys) Dipnoi (lungfishes) Amphibia (frogs, salamanders) Reptilia (turtles, snakes crocodiles, birds) Mammalia (mammals) Dorsal nerve cord, notochord, pharyngeal gill slits, post-anal tail Vertebral column Jaws Lungs Skull Lobed fins Limbs Amniotic egg Hair, milk An Evolutionary Tree of the Chordates Fig. 24-1
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Chordate Features in the Human Humans are members of the phylum Chordata In humans, the chordate features are best seen during embryonic development, but later, we lose our notochord, gill slits, and tails Only the dorsal nerve cord is retained in post embryonic human development Fig. 24-2
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Comparison of Vertebrate Embryos
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24.2 Which Clades Make Up the Chordates? The chordates include 3 clades 1. The lanceletes 2. The turnicates 3. The craniates 1: LANCELETS are marine filter-feeders Lancelets are small, fishlike, invertebrate chordates that retain all the four chordate features as adults Lancelets live half-buried in the sand, with only the anterior end of their bodies exposed Food particles are drawn into the mouth by pharyngeal cilia and are then transported to the digestive track
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Author Animation: The Phylum Chordata
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(a) Lancelet nerve cord notochord gut muscle segments tail anus gill slits mouth Invertebrate Chordates Fig. 24-3a
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2: TUNICATES include sea squirts and salps Tunicates (sea squirts) live in a marine environment The larvae are motile & exhibit all key chordate features Adults are sessile filter-feeders that have lost their tail and notochord Barrel-shaped tunicates, known as salps, live in the open ocean and move by contracting an encircling band of muscle that propels that organism forward
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Author Animation: Lancelets and Tunicates
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3: CRANIATES have a skull – The craniates include all chordates that have a skull that encloses a brain – This group includes the hagfish and the vertebrates- animals in which the embryonic notochord is replaced during development by a backbone, or vertebral column , composed of bone or cartilage (which resembles bone, but is more flexible) 1. Supports the body 2. Provides attachment sites for muscles 3. Protects nerve cord and brain
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Hagfishes are slimy residents of the ocean floor They lack jaws They are exclusively marine, and live near the ocean floor They feed primarily on worms
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