The members of Class Amphibia (Gr., Amphi : dual, bios, life) can live in aquatic as well as terrestrial habitats.
Examples:
 |  |  |
| Bufo (Toad) | Rana (Frog) | Hyla (Tree frog) |
 |  |
| Salamandra (Salamander) | Ichthyophis (Limbless amphibia) |
Body characteristics:
- Body is divisible into head and trunk (tail is present in some of them). But neck is absent.
- Trunk bears two pairs of limbs. Digits are without claws.
- The amphibian skin is smooth and moist (without scales) due to the presence of mucous glands.
- The eyes are provided with movable eyelids and a nictating membrane (third eyelid). The nictating membrane is a water-proof covering used when the animal is in water.
Evolution of An Amphibian
- A tympanum represents the ear.
- Alimentary canal, urinary and reproductive tracts open into a common chamber called cloaca which opens to the exterior.
- Respiration is by gills, lungs and through skin.
- The heart is three–chambered (two auricles and one ventricle). Hence, there is mixing up of oxygenated and deoxygenated blood inside the heart.
Physiology: These are cold-blooded animals (poikilotherms).
Reproduction: Sexes are separate. Fertilisation is external (mostly in the water). They are oviparous and development is indirect. Larval stage has a tail, and is mostly aquatic.
