Amphibians
Class Amphibia:
 
  • Amphibians have smooth moist skin. The toad is an exception with rough dry skin.
  • The majority of amphibians contain four limbs with no claws on their digits (toes).
  • They contain a three chambered heart. Two atria and one ventricle. There is a possibility of the oxygenated and unoxygenated blood mixing in the ventricle.
  • They are ectotherms. During extreme environmental conditions they either hibernate (winter) or aestivate (summer).
  • They carry on external fertilization. Their offspring develop through a process called metamorphosis. Tadpoles (aquatic larvae) resemble fish. Over a period of time they change in form into the adult amphibian.
  • They respire through poorly developed lungs and moist skin.
  • They contain a well developed muscular system.
  • The digestive system is adapted to digest whole prey, swallowed by the organism.
  • Two kidney's rid the body of nitrogenous waste. The amphibian liver carries on several functions: detoxifying poisons, producing bile, and storing glucose in the form of glycogen.
  • The cloaca is a sac that collects discharge from the large intestine, urinary bladder, and gonads before it is eliminated from the body.
  • Their brain is well developed and is attached to a dorsal nerve cord.
  • Most amphibians contain three eye lids. Two are normal and one is transparent.
  • These are the first animals to possess a pressure releasing canal called the Eustachian tube. The tube connects the mouth cavity with the tympanic membrane.
 
Orders of Amphibia:
 
Order Apoda. This order contains amphibians without legs. Examples of this order are the caecilians. Most of these organisms live in the moist soil, while some tropical species live in ponds and streams.
 
Order Urodela. These are tailed amphibians. Included in this group are the salamanders and newts. These animals contain a tail and neck. Some of these organisms never develop lungs and must rely on external gills.
 
Order Anura. Frogs and toads represent these tailless organisms. Frogs use powerful hind legs for movement. Their long sticky tongue is attached to the tip of the lower jaw. They exhibit a variety of colorful skin, which is sometimes poisonous. Frogs live in many areas of the world. The male is the only one of the species that makes sounds.
 
Tadpole and Adult Comparison
Characteristics
Adult Frog
Tadpole
Type of limbs
legs
fins
Heart chambers
3
2
Type of food
Carnivorous
Vegetarian
Respiratory structure
Lungs and Skin
Gills