Amphibians, members of the class Amphibia, include frogs, toads, salamanders, newts and caecilians.
These animals are all vertebrates and are all cold-blooded (ectothermic).
Amphibians are tetrapods.
The amphibians that are alive today are divided among three orders.
Anura comprises frogs and toads.
Caudata consists of salamanders and newts.
Caecilians make up the order Gymnophiona.
The Caecilians are a group of legless burrowing amphibians. They are difficult to find. Therefore, we do not know much about them.
Amphibians lay their eggs in water.
After an amphibian hatches, it lives in water and breathes through gills.
The young amphibian must undergo metamorphosis in order to become an adult.
Most amphibians live on land when they are adults.
Amphibians usually have no legs in the juvenile stage and four legs in the adult stage.
However, some juvenile salamanders and newts have legs.
Adult caecilians have no legs. They look like earthworms.
All amphibians secrete toxins from their skins. This helps to protect them from predators.
The name "amphibian" is Greek for "both lives". The name comes from the fact that amphibians have two different "lives" - a life in a juvenile form, in water, before metamorphosis and a life in an adult form, usually on land, after metamorphosis.
The largest amphibian in the world is the Chinese giant salamander, which can grow up to 6 feet long and weigh 140 pounds.
The Brazilian gold frog and the Monte Iberia eleuth - another frog - are the world's smallest amphibians. Both are under 1/3 of an inch long.
Before they undergo metamorphosis, amphibians use gills to breathe oxygen in water.
Adult amphibians usually lose their gills.
Mudpuppies - a type of salamander - breathe with gills their entire lives.
Most adult amphibians get oxygen from the air by breathing with lungs.
Adult amphibians can also breathe through their skins. Oxygen from the air and from water passes directly through the skin into blood vessels just under the surface of the skin.
Breathing through the skin is known as cutaneous respiration.
Some adult amphibians have very small lungs, and some have no lungs at all.
They are able to obtain enough oxygen through cutaneous respiration.
The skin of an amphibian must remain moist in order for the amphibian to be able to breathe through its skin.
An adult amphibian has glands that produce mucus, which helps to keep its skin moist.
Amphibians must spend their lives around water so that their skin stays moist.
They often live near fresh water or brackish water (water that is more salty than freshwater but less salty than seawater) - for example, near lakes, ponds, streams and puddles. They cannot tolerate seawater.
Sometimes an amphibian will keep its skin moist by staying in a damp place, such as underneath a damp, rotting log, or by burrowing underground.
There are amphibian species that live in deserts and are able to obtain enough moisture to survive.
Some amphibians estivate when their environment becomes dry. During estivation, an animal's metabolism slows down.
Estivation takes place in dry or hot environments. It is similar to hibernation, which is a slowing down of metabolism that occurs in cold environments. Some amphibians hibernate when the temperature becomes. too cold.
Amphibians are very sensitive to changes in their environment. When a change in environment, such as a change in climate, takes place, it often affects amphibians before it affects other types of animals. Therefore, many species of amphibian are often considered indicator species - species that provide an indication of the overall health of the habitats in which they live.