eel
Eels are ray-finned fish in the order Anguilliformes which consist of about 800 species. They are elongated fish that range in length from 5 cm (2.0 in) to 4 meters (12 feet). Most of these animals live in shallow waters and burrow into sand, mud, or hide amongst rocks. The majority of eels are nocturnal creatures and some species live in deep waters at depths of up to 4,000 meters (13,000 feet).