Lecture 23 – Vertebrata – Tetrapoda

Lecture 23 – Vertebrata –...

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Lecture 23 – Vertebrata – Tetrapoda Tetrapoda refers to land dwellers (means “four legs”) A. Amphibia (fig. 31-18) – means “two lives;” a number of frogs and toads must return to the water for reproduction so they aren’t complete land dwellers 1. Frogs, toads, salamanders 2. Lung fishes – amphibians evolved from these 3. Return to water – for reproduction; fertilization is external (frogs are oviparous) – the eggs are fertilized and laid in the water and a tadpole develop 4. Metamorphosis 1) Tadpole – completely dependent on the water (fish-like tail, gills, lateral line organ: characteristic of fish); amphibians are the first group from the fish so they are very fish-like 2) Develop the fins, tail is reabsorbed 3) Develop into the adult frog (which is more terrestrial than aquatic) 5. Thyroid gland – directs metamorphosis 6. Respiration – have very simple lungs (a simple sac, no lobes like ours), also have skin for air exchange (it is highly vascularized, which means there are a lot of blood vessels going to it) and this is why the frog must be moist, anything that uses skin as a means for respiration must be moist
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Lecture 23 – Vertebrata –...

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