Phylum Chordata: Class Amphibia

Class Amphibia

The world of amphibians include frogs, toads, salamanders, and newts. Amphibians spend part of their life cycles in the water and on land. They depend on having a moist habitat. They are cold-blooded and have thin skin which they use to breathe with and absorb water.

Posion Dart Frog

They reproduce sexually with either internal or external fertilization. Eggs are placed under water so that they won't dry out. They are covered with a jelly like substance which helps to keep moisture inside and protect them from predators.

They have a closed circulatory system, with a three chambered heart--two atria and one ventricle. Oxygen-low blood circulates to the heart and is pumped into the lungs where it gets replenished with oxygen (pulmonary circulation). Then, it goes back to the heart where it is pumped to the rest of the body through blood vessels (systematic circulation). Because there is only one ventricle, there is some mixing of deoxygenized and oxygen-rich blood, this makes oxygenation slow. There is a ridge in the ventricle that helps to separate the two bloods.