Notochord – flexible rod that extends down the length of the body Invertebrate chordates – notochord becomes skeleton Vertebrate chordates – notochord disintegrates Chordates are named after a structure that is found in all chordate embryos
All chordates have: 1. Notochord 2. Hollow nerve cord – develops into brain and spinal cord 3. Pharyngeal slits – become gills in fish; not present in the adults of reptiles, birds, and mammals 4. Post-anal tail
Characteristics of Vertebrates Skull – protect brain Backbone – protect nerve cord Vertebrae – skeletal segments that compose the backbone Vertebrae can be made up of cartilage (sharks) or a combination of bone and cartilage (humans) shark vertebrae human vertebrae
The evolution of hinged jaws enabled vertebrates to capture and eat a wide variety of prey
How do Gills Function? Hemoglobin is a protein in blood that binds readily with oxygen The blood moving in the capillaries in the blood is very low in oxygen There is a higher concentration of oxygen in the surrounding water than in the capillaries Diffusion! Oxygen diffuses across the membranes of the gills into the capillaries
Fishes with Bony Skeletons Bony fishes have a stiff skeleton reinforced by calcium compounds Operculum – protective flap which covers the gills; movement of the flap flushes water over the gills Internal Air Sac – makes the animal more buoyant
Fishes with Cartilaginous Skeletons Cartilage – tough, elastic connective tissue that allows smooth movement Sharks & Rays are cartilaginous fishes *Shark dissection the week after Spring Break! Rays are bottom-dwellers that use their jaws to crush mollusks and crustaceans Tail is used for defense
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