Amphibians are amniotes.  They have appendages adapted for terrestrial mobility; they have four legs that is why they are called tetrapods.  Aquatic larvae metamorphose into terrestrial adults in many species of Amphibia.  Amphibians may lay eggs or bear live offspring.  They can respire via their lungs and/or through their skin.  All have a three chambered heart.

Urodela.  These are tailed amphibians such as salamanders.

Anura.  These are tail-less amphibians such as frogs and toads.

Apoda.  These are legless amphibians such as the caecilians.

The Amniotic Egg

amnion:  protects the embryo allantois:  disposal sac allantois + chorion = gas exchange Note:  Placental mammals retain the 4 extra-embryonic membranes (amnion, allantois, chorion, yolk sac)

Next:  "Reptiles."