Batrachochytrium dendrobatidis is a non-filamentous, aquatic chytrid fungus. Chytrids are unique among true fungi in that they produce uniflagellated zoospores. No resting spore or sexual stages are known for Batrachochytrium dendrobatidis. Chromosome copy number variation is widespread in this species and the genome of individual isolates may contain 2 to 5 copies of each chromosome. Batrachochytrium dendrobatidis, known as the amphibian chytrid, is an amphibian pathogen that causes chytridiomycosis; this disease is implicated as the primary cause of the recent declines of frog populations around the world. Batrachochytrium dendrobatidis infects the skin of frogs, causing thickening of the keratinized layer. It is the only chytrid species known to parasitize vertebrates.