The caecilians are an order (Gymnophiona) of amphibians that superficially resemble earthworms or snakes. They mostly live hidden in the ground, making them the least familiar order of amphibians. All extant caecilians and their closest fossil relatives are grouped as the clade Apoda. They are mostly distributed in the tropics of South and Central America, Africa, and South Asia. The diets of caecilians are not well known.