Leptocephalus

A leptocephalus (meaning "slim head") is the flat and transparent larva of eels and other members of the superorder Elopomorpha. This is one of the most diverse groups of teleosts, containing 801 species in 4 orders, 24 families, and 156 genera. This group is thought to have arisen in the Cretaceous period over 140 million years ago. Fishes with a leptocephalus larval stage include the most familiar eels such as the conger, moray eel, and garden eel as well as members of the family Anguillidae, plus more than 10 other families of lesser-known types of marine eels. These are all true eels of the order Anguilliformes. Leptocephali of eight species of eels from the South Atlantic Ocean were described by Meyer-Rochow. The fishes of the other four traditional orders of elopomorph fishes that have this type of larvae are more diverse in their body forms and include the tarpon, bonefish, spiny eel, pelican eel and deep sea species like Cyema atrum and Notacanthidae species, the latter with giant Leptocephalus-like larvae.