Amphibians are animals with moist, hairless skin through which water can pass in and out. The majority of amphibians live the first part of their lives in water and the second part on land. This reflects the name amphibian which comes from the Greek words amphi, meaning “both,” and bios, meaning “life.”
There are three main groups of amphibians; frogs and toads, salamanders, and caecilians, and scientists recognize more than 4,000 species of amphibians. There are over 3,500 species in the Frogs and Toads category, and 360 in the salamander group. The Caecilians group is the smallest, and has about 160 species, and they are the rarest of amphibians.
The largest amphibian in the world today is the Chinese giant salamander, which can reach up to six feet in length.
The term "amphibian" is also sometimes used to refer to a seaplane.
Starting in the 1900s, large declines of amphibian populations were noticed. This was identified to be caused by a pathogenic fungus, Batrachochytrium dendrobatidis (Bd), after an outbreak in 1998. Bd primarily infects keratinous areas of anurans, namely the mouthparts of tadpoles and the hind limbs of adults. Costa Rica has shown considerable declines, with extinctions of some species, such as the golden toad.