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Lab 8 Handout

Lab 8 Handout - AnimalDiveristyIII:Craniata Introduction...

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Animal Diveristy III: Craniata Introduction This week we will finish our sampling of animal diversity with the Craniata. Consider many of the trends you have already seen in organisms with bilateral symmetry. In this clade you will see increased cephalization. Our focus this week is on the Vertebrata. Some of the salient points to consider when making observations in this lab are: adaptations associated with the water to land transition, feeding morphology, and changes in limb morphology. Craniata (Hagfish and Vertebrates) The Craniata includes nine extant clades. Six of these (Myxini, Cephalaspidomorphi, Chondrichthyes, Actinopterygii, Actinista, and Dipnoi) are collectively called “fishes.” The other three classes (Amphibia, Sauropsida [which includes the subclass Aves], and Mammalia) are the tetrapods and are primarily terrestrial. The common names for the six fish clades are hagfish, lampreys, cartilaginous fishes, ray finned fishes, lobe‐finned fishes, and lungfishes. This week’s lab will include hagfish and lampreys. We will examine the other groups in the third lab on animal diversity. Vertebrata Traditionally, the subphylum vertebrata has included the hagfish. This creates on small problem: the hagfish do not have true vertebrae. As a result, the term “Craniata” is used to designate a larger clade which includes the vertebrates, along with hagfish. The craniates are distinguished by having a cranium: a skull made of cartilage or bone that protects the brain. Vertebrates can then be classified as animals with a backbone composed of vertebrae. Craniates also share the character of neural crest tissue, the chunk of neural ectoderm that rolls up to form the dorsal nerve tube. Craniate embryos form this neural crest tissue, and no other animal group does. The brain tissue develops embryologically to form just about the entire vertebrate head, including most of the brain, the central nervous system, the brain case, most of the sense organs, cartilaginous gill arches (which becomes parts of the circulatory system, middle ear bones, and jaws), and teeth. Characteristics of Vertebrates Traditionally, the subphylum vertebrata has included the hagfish and lampreys. This creates on small problem: the hagfish and lampreys do not have true vertebrae. As a result, the term “Craniata” is used to designate a larger clade which includes the vertebrates, along
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with hagfish and lampreys. The craniates are distinguished by having a cranium: a skull made of cartilage or bone that protects the brain. Vertebrates can then be classified as animals with a backbone composed of vertebrae. Craniates also share the character of neural crest tissue, the chunk of neural ectoderm that rolls up to form the dorsal nerve tube. Craniate embryos form this neural crest tissue, and no other animal group does. The brain tissue develops embryologically to form just about the entire vertebrate head, including most of the brain, the central nervous system, the
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