BIOL108 Lecture Notes - Lecture 2: Squamosal Bone, Hagfish, Middle Ear

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BIOL108 Full Course Notes
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BIOL108 Full Course Notes
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In a deuterostome, the eight-cell stage is radial and indeterminate (stem cells); cells can become different things given different conditions: anus develops first, contains both invertebrates and vertebrates. All are present in all species but in many cases, they are highly modified beyond recognition or lost when they become adult. The same hox genes code for nerve cords in vertebrates and invertebrates. Modification of pharyngeal slits in vertebrates: turn into jaws. In mammals, they turn into jaw, teeth, parts of skull, tonsils, parathyroid glands, and eustachian tubes and aid in hearing. Movement, better able to get food and energy (filter feeding), higher levels of activity. Cephalochordates and urochordates (invertebrates): nonvertebrate chordates, cephalochordates retain all 5 derived characteristics in adult form, urochordates only retain pharyngeal slits as an adult. They are sedentary and stick to ocean floor: pharyngeal slits for filter feeding (common to both cephalochordates and urochordates) Vertebrates: over 60,000 species, most of them are fishes, extremely successful on land.

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