Kingdom: Animalia Phylum: Chordata Class: Actinopterygii Subclass: Neopterygii Infraclass: Teleostei Superorder: Elopomorpha Order: Anguilliformes Berg, 1940 Suborders Anguilloidei Congroidei Nemichthyoidei Synaphobranchoidei Eels (Anguilliformes; pronounced /wlfrmiz/) are an order of fish, which consists of four suborders, 19 families, 110 genera and approximately 800 species. Most eels are predators. The term "eel" is also used for some other similarly shaped fish, such as electric eels and spiny eels, but these are not members of the Anguilliformes order. Description Eels are elongated fish, ranging in length from 5 centimetres (2.0 in) in the one-jawed eel ( Monognathus ahlstromi) to 4 metres (13 ft) in the slender giant moray.[2] Adults range in weight from 30 grams to well over 25 kilograms. They possess no pelvic fins, and many species also lack pectoral fins. The dorsal and anal fins are fused with the caudal or tail fin, forming a single ribbon running along much of the length of the animal.[1] Most eels live in the shallow waters of the ocean and burrow into sand, mud, among rocks, or in cracks found in coral reefs. A majority of eel species are nocturnal, and thus are rarely seen. Sometimes, they are seen living together in holes, or "eel pits". Some species of eels also live in deeper water on the continental shelves and over the slopes deep as 4,000 metres (13,000 ft). Only members of the Anguillidae family regularly inhabit fresh water, but they too return to the sea to breed. [3] Eels begin life as flat and transparent larvae, or leptocephali. Eel larvae drift in the surface waters of the sea feeding on marine snow, small particles that float in the water. Eel larvae then metamorphose into glass eels and then become elvers before finally seeking out their juvenile and adult habitats.[2] Classification A moray eel. Juvenile American eels Garden eels This classification follows FishBase in dividing the eels into fifteen families. Additional families that are included in other classifications (notably ITIS and Systema Naturae 2000) are noted below the family with which they are synomized in the Fish Base system. The origin of the fresh water species has been problematic. Genomic studies indicate that they are a monophyletic group which originated among the deep-sea eels