General characteristics

• These are partly aquatic and party terrestrial.
• Their thin smooth skin is supplied with numerous blood vessels which permit intake of oxygen to supplement the rather small amount obtained by the lungs.
• Their skin has no scales.
• Their heart is three chambered.
• Fertilization is external. The aquatic larvae which is known as tadpole undergoes metamorphosis into terrestrial adult.
• Their body has distinct head and trunk but no neck. Examples Frogs, toads, salamander.

External and internal features of a frog

External features of frog’s body

Skin: loose-fitting smooth and slimy skin with mucous glands.

Head: bears a wide mouth, a pair of nostrils and protruding eyes.

Ear drum: for sensation of sound waves.

Internal features of a frog

Fat bodies are spaghetti shaped structures that have a bright orange or yellow color look like.

Liver is brown colored organ found behind the heart.

Esophagus is found behind the glottis.

Rugae found in the digestive system.

Life cycle

Adult frogs return to water to reproduce, laying their eggs directly in water. Eggs are fertilized externally and hatch into swimming larvae forms called tadpoles. Tadpoles live in the water, where they feed on minute algae. After considerable growth, their body abruptly changes into that of adult frog. Tail, gills, and lateral line system disappear, and legs grow from the body. The mouth broadens, developing teeth and jaws.