2. Amphibians

3. Amphibians  Vertebrate (backbone)  Ectothermic (cold- blooded)  Must absorb heat from external sources  When environment becomes too hot or too cold, many amphibians become dormant (inactive or at rest) by burrowing in the mud.

4. Amphibians: Metamorphosis  All amphibians begin life in water  Most amphibian eggs are fertilized externally  Eggs do not have shells (moist; must lay in water)

5. Amphibians: Metamorphosis  Fertilized eggs hatched into tadpoles (larval stage)  Tadpoles have fins, gills, and a 2-chambered heart  Tadpoles develop into adults  Develop legs, lungs, and a 3-chambered heart

6. Amphibians: Respiration  Tadpoles obtain oxygen from water that passes over gills  Adults have lungs so that they can exchange gases with the air  Adults also exchange gases through their thin, moist skin Salamander tadpole with feathery gills extended

7. Amphibians: Circulation  Tadpole – 2- chambered heart and a single loop of vessels  Adult – 3-chambered heart and two loops of vessels (needed for life on land)

8. Types of Amphibians:  Order Anura – frogs & toads  Do not have tails; feed on insects and worms; have jaws and teeth; frogs have long legs and smooth skin; toads have bumpy skin and short legs

9. Types of Amphibians:  Order Caudata – salamanders  Long, slender body with neck and tail; smooth, moist skin and no claws; some live in water, others in damp places; hatch from eggs, adults are carnivorous

10. Types of Amphibians  Order Gymnophiona – caecilians  Burrow into the ground; no limbs; short or no tail; live in warm, tropical climates; usually blind; eat earthworms; internal fertilization

11. Comparison of Hearts