AMPHIBIANS

Characteristics - There are three types of amphibians:

Urodeles (tailed): Some of these amphibians are entirely aquatic, but others live on land as adults or throughout their entire life. An example of a Urodeles is a salamander.

Anurans (no tail): These are more specialized than the Urodeles for motion on land. For example, frogs use their powerful hind legs to hop on land and eat by catching insects with their long, sticky tongue.

Apodans (no legs): Nearly blind and superficially resemble earthworms. Most live in tropical areas, some live in freshwater ponds and streams. The tadpole stage of frogs is usually aquatic. Apodans are herbivores with internal gills and a long finned tail. This type does not have legs.

"Amphibian" means 2 lives, and is a reference to the metamorphosis that many amphibians undergo (tadpole-frog). During the "2nd life", the process of metamorphosis develops legs, however, gills and lateral line systems disappear. By now, they have air-breathing lungs, external eardrums and a digestive system. Not all amphibians go through the aquatic stage and many do not live a dualistic life. In all 3 orders there are terrestrial and aquatic only animals.

Reproduction:
Fertilization is external in most species. Amphibians lay their eggs in ponds or swamps Some species must lay vast numbers of eggs because mortality is high depending on the species. Depending on the species, either the males or the females can incubate the eggs on their backs, stomachs, or even their mouths.

 

Respiration:
Amphibians use both gills and lungs for gas exchange. The gills are used while underwater; O2 comes out of the water and into the gills, and Co2 goes out with the expulsion of water. While on land, the lungs are used, and if the skin of the amphibian is kept moist, the animal can breathe through it's skin. Lungs are used by most adult amphibians as a means of respiration.

Circulation:
Amphibians have a 3-chamber heart, which is more efficient then that of the fish, but is still rather inefficient as the oxygenated and deoxygenated blood can mix within the ventricle. The amphibian heart has a double pump. The blood from the body comes in through the right atrium, and that of the lungs comes from the left atrium, the blood then is pumped into the ventricle, where it mixes and is pumped back to the body of the amphibian and its lungs. The path that pumps blood to the lungs and skin is the pulmonary circuit, where blood picks up oxygen as it flows through capillaries. This blood then gets pumped into the systematic circuit, which carries blood to all other organs. The use of both these circuits is called double circulation, and this ensures a vigorous flow of blood to the brain, muscles and other organs because the blood is pumped a second time.

Excretory System
The kidneys of amphibians function much the same as those of fresh water fish. When in fresh water, the skin of the frog accumulates certain salts from the water by active transport, and the kidneys excrete dilute urine. On land, where dehydration is the most pressing problem, frogs conserve body fluid by reabsorbing water across the epithelium of the urinary bladder. Amphibians that undergo metamorphosis generally switch from excreting ammonia to urea during the transformation from an aquatic larva, the tadpole, to the terrestrial adult.

Feeding Adaptations
A frog nabs insects by flicking out its long sticky tongue that is attached to the front of the mouth. Adult frogs are carnivores. They have a small number of teeth that line the margins of the upper jaw. Frogs also have certain adaptations that help them from being eaten. Certain colour patterns camouflage amphibians from predators. Also some amphibians have skin glands that secrete distasteful, or even poisonous mucus.

Endoskeleton
In some ways, the amphibian's (frogs for example) skeleton resembles that of a fish. Yet the frog has many adaptations for living on land. In frogs, the number of vertebrates are small and there are no ribs. The frog skeleton is most different from that of a fish in the bones that support the anterior and posterior limbs. The pectoral girdle attaches the front limbs to the body. The rear limbs are attached by the pelvic girdle.

Other images of amphibians


Frog links: Thinkquest and a collection.

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