Amphibians are a distinct group of vertebrates that typically share a few defining traits: they usually have smooth, moist skin through which water and gases can pass; they are ectothermic (cold-blooded), relying on environmental heat to regulate body temperature; many species undergo metamorphosis (e.g., a larval aquatic stage with gills and tails that becomes an air-breathing, typically legged adult); and they commonly live life tied to moist environments, occupying both aquatic and terrestrial habitats at different life stages. Key features that make an animal an amphibian

• Skin and respiration: Amphibians have permeable, moist skin that can absorb water and some oxygen directly through the skin, supplementing or replacing lungs in many species. This skin is a critical interface with their environment and also a site of vulnerability to drying and pollution.

• Temperature regulation: They are ectotherms, meaning their body temperature follows the ambient environment rather than being internally controlled. This often shapes their behavior and habitat choices.

• Life cycle and metamorphosis: Most amphibians begin life in water as eggs laid in moist environments, hatch into aquatic larvae (often gilled and tailed, like tadpoles), and undergo metamorphosis to become air-breathing adults with legs. This dual life in water and on land is a hallmark of the group, though there are exceptions.

• Habitat use: Amphibians typically require moist or aquatic environments for reproduction and early development, and many species later occupy terrestrial habitats as adults. Their life cycles often tie them to wet habitats at certain life stages.

• Classification notes: The group includes creatures commonly known as frogs, toads, salamanders, and caecilians, though the classic traits above apply across these diverse lineages.

Additional context and nuances

• Not all amphibians are strictly tied to water all their lives, especially as adults; many species spend substantial time on land, returning to water mainly to breed. Their reliance on moist skin makes them particularly sensitive to environmental changes, pollutants, and habitat loss.

• Some educational resources emphasize a combination of the four broad traits—moist skin, ectothermy, life cycle involving metamorphosis, and dual aquatic-terrestrial habitat use—as the core criteria for identifying amphibians. Different sources may highlight additional specifics, such as lifecycle timing, respiration methods, or ecological roles.

If you’d like, I can tailor this to a particular audience (kids, students, or a quick field guide) or compare amphibians to closely related vertebrates to highlight what sets them apart.