The chytrid fungus Batrachochytrium dendrobatidis is a recently described species that has been responsible for the total extinction of populations and species of amphibians worldwide. The group of chytridiomycete fungi is well known through genera that parasitize invertebrates and plants. They are found all over the world, in all environments including areas well conserved and very sensitive to contamination. The recently described amphibian chytrid species is unique in being the first case of a chytrid fungus that affects a vertebrate. The amphibian populations affected by this species of fungus (known as the "assassinator fungus") generally disappear in a few consecutive months, following a pattern of dispersion that is typical of infectious diseases. The adults (change to recent metamorphs) die rapidly while the larvae, which are only infected in their mouthparts die later when the keratin (and with this the fungus) extends over the entire body at the completion of metamorphosis. Once the fungus has appeared in a zone it appears to stay in the environment as a saprophyte, even when the amphibians have disappeared. The ultimate cause of mortality of infected animals is not known for sure but the development of the disease (known as chytridiomycosis), always affects the superficial layers of the skin and never the internal organs. When the zoospores (flagellated mobile spores) come into contact with amphibian skin they attach and in a few days develop into zoosporangia that generate new zoospores. The spores have no operculum and the zoospores are released through a discharge tube which perforates the skin of the infected animal. Chytrdiomycosis was originally detected a few years ago in Australia and Central America, but today it is distributed across the globe, including Spain.