amfibian

Amfibian, often written as amphibian in English, refers to members of the class Amphibia, a diverse group of cold-blooded, tetrapod vertebrates that typically rely on both aquatic and terrestrial environments during their life cycle. The class includes three orders: Anura (frogs and toads), Caudata/Urodela (salamanders and newts), and Gymnophiona (caecilians).

Amphibians are characterized by their permeable skin, which can absorb water and oxygen, making them highly dependent on moist habitats. They are ectothermic, with body temperatures influenced by the environment. Adult amphibians generally have limbs, with variations in limb structure across the three orders, and most undergo metamorphosis from aquatic, gilled juveniles to air-breathing adults, though some lineages exhibit direct development without a free-swimming larval stage or retain juvenile features into adulthood (paedomorphosis).

Reproduction typically requires water or very damp environments. Eggs are usually laid in water and hatch into aquatic larvae (tadpoles in frogs and many other groups), which then metamorphose into terrestrial or semi-aquatic adults. Diets vary but often include invertebrates; adults are primarily carnivorous, and larval forms may have different feeding habits.

Amphibians play important ecological roles as both predators and prey and are considered sensitive indicators of environmental health due to their permeable skin and aquatic dependencies. The fossil record dates amphibians to roughly 370 million years ago, making them among the earliest terrestrial vertebrates.

Conservation concerns are significant: habitat loss, pollution, climate change, invasive species, and fungal diseases such as chytridiomycosis (caused by Batrachochytrium dendrobatidis) have led to declines in many species. Efforts focus on habitat protection, pollution reduction, disease management, and monitoring population trends.