Short answers, pulled from the story.
Amphibians are ectothermic, anamniotic, four-limbed vertebrates that make up the class Amphibia. All living amphibians belong to the subclass Lissamphibia, which has three orders: Anura (frogs and toads), Urodela or Caudata (salamanders), and Gymnophiona or Apoda (caecilians).
Following the classification by Darrel Frost and the American Museum of Natural History, the total number of known living amphibian species as of the 31st of March 2019 was exactly 8,000. Nearly 90% of them are frogs.
Adult amphibians generally cannot breathe underwater. Wildlife hospitals report that people often place frogs and toads in water-filled aquaria with no way to climb out, and as a result the animals may drown. Amphibians do use their permeable skin as a secondary respiratory interface.
The smallest amphibian and smallest known vertebrate is Paedophryne amauensis, a frog from New Guinea measuring just 7.7 mm. The largest living amphibian is the 1.8 m Chinese giant salamander, Andrias davidianus, while the largest amphibian that ever existed, the extinct Prionosuchus, reached up to 9 m.
The first major amphibian groups appeared in the Devonian period, around 370 million years ago, descending from lobe-finned fish similar to modern coelacanths and lungfish. These fish had leg-like fins with digits and primitive lungs, and Ichthyostega was one of the first primitive amphibians with nostrils and more efficient lungs.
Amphibians are ecological indicators because of their permeable skins and complex reproductive needs, which make them sensitive to habitat conditions. In recent decades there has been a dramatic decline in amphibian populations for many species around the globe.