According to the taxonomy of living things, the phylum chordata (animals with backbones) is divided into five classes: fish, amphibians, reptiles, mammals and birds. The class of amphibians includes frogs, toads, salamanders, newts and caecilians. An amphibian is a cold-blooded vertebrate born in water where it breathes through gills. As the larva undergoes metamorphosis and develops into an adult, its lungs gain the capacity to breathe air, and the animal can survive on land. As an example, here are the stages in the life cycle of a frog. An adult frog will lay up to 1500 eggs at a time, which then group together in a jelly-like substance and float on the water surface until they hatch in about 1-3 weeks. Emerging from the eggs, the larval form, called a tadpole, will first develop gills, then legs. It will then grow arms and become a froglet. Finally it will absorb its tail back into its body to become an adult frog. The entire process takes approximately 12 weeks from eggs to adult. Characteristics of Amphibians Vertebrates: Every amphibian has a backbone. This backbone begins as cartilage, and changes as the rest of the organs undergo metamorphosis. External Fertilization: Amphibians do not need to mate before releasing their eggs into the water. They reproduce by laying transparent eggs with a jelly-like texture that are later fertilized by the male. Cold Blooded: Amphibians, like reptiles and fish, are cold-blooded. They can't control their body temperature, but must rely on sunlight or shade as needed, to alter or maintain their internal temperature. Carvivorous: Amphibians are carnivores. Primitive lungs: The lungs of all amphibians change during metamorphosis. They t serve as gills while the animal is submerged, but as adults, they allow them to breathe straight through the skin. Live on water and land: When amphibians are born, they spend their first days in the water. After their metamorphosis they will reside mostly on land, but still require a damp habitat. Resources HTML & design by Bill Willis 2024