What is "leptocephalus"

n. the larva of an eel, flat in shape and transparent

1. n. slender transparent larva of eels and certain fishes

2. [also: leptocephali (pl)]

Leptocephalus (meaning "slim head") is the flat and transparent larva of the eel, marine eels, and other members of the superorder Elopomorpha. This is one of the most diverse groups of teleosts, containing 801 species in 24 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. 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, and pelican eel.

Leptocephalus is a genus that was used for species of larval eels, called leptocephali, that were thought to be new fish species, or whose adult eel species were not known. Leptocephali differ so much in appearance from their adults that the larvae and adults of eels are not easily matched, and when first discovered, leptocephali were thought to be a different type of fishes, but not eels. Because of this, the genus designation of Leptocephalus was used for a while for unidentified leptocephali even after it was known that these were the larvae of eels thus becoming a " wastebasket taxon", but this practice is no longer used. Examples of marine congrid larvae, found in the western Indian Ocean and the Red Sea that were named this way are listed below. Only two species (L. bellottii and L. ophichthoides) in two different families are currently treated as having any validity though that of L. bellottii is strongly in doubt.