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 distinct 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 in two families are currently treated as having any validity, though the validity of L. bellottii is strongly in doubt.
Nettenchelys is a genus of eels in the duckbill eel family Nettastomatidae.
Ariosoma bauchotae is an eel in the family Congridae. It was described by Christine Karrer in 1983. It is a marine, deep water-dwelling eel which is known from waters northwest of Madagascar, in the western Indian Ocean. It is known to dwell at a depth range of 308–314 metres.
Ariosoma meeki is an eel in the family Congridae. It was described by David Starr Jordan and John Otterbein Snyder in 1900, originally under the genus Congrellus. It is a subtropical, marine eel which is known from Japan and the Peng-hu Islands, in the northwestern Pacific Ocean. Males are known to reach a maximum total length of 53 centimetres.
Ariosoma multivertebratum is an eel in the family Congridae. It was described by Emma Stanislavovna Karmovskaya in 2004. It is a marine, deep water-dwelling eel which is known from the Marquesas Islands, in the eastern central Pacific Ocean. It is known to dwell at a depth range of 300–460 metres. Males can reach a maximum total length of 54.2 centimetres.
Ariosoma sazonovi is an eel in the family Congridae. It was described by Emma Stanislavovna Karmovskaya in 2004. It is a marine, deep water-dwelling eel which is known from the Philippines, in the western Pacific Ocean. It is known to dwell at a depth range of 160–440 metres. Females can reach a maximum total length of 39.5 centimetres.
Ariosoma sereti is an eel in the family Congridae. It was described by Emma Stanislavovna Karmovskaya in 2004. It is a marine, deep water-dwelling eel which is known from the Marquesas Islands, in the eastern central Pacific Ocean. It is known to dwell at a depth range of 95–370 metres. Females can reach a maximum total length of 26.5 centimetres.
Parabathymyrus fijiensis is an eel in the family Congridae. It was described by Emma Stanislavovna Karmovskaya in 2004. It is a marine, deep water-dwelling eel which is known from Fiji, in the western Pacific Ocean. It dwells at a depth range of 478–500 metres. Females can reach a total length of 36 centimetres.
Acromycter longipectoralis is an eel in the family Congridae. It was described by Emma Stanislavovna Karmovskaya in 2004. It is a marine, deep water-dwelling eel which is known from New Caledonia, in the western Pacific Ocean. It is known to dwell at a depth of 580 metres. Females can reach a total length of 21.7 centimetres.
The Bullish conger is an eel in the family Congridae. It was described by David G. Smith and Robert H. Kanazawa in 1977, originally under the genus Rhechias. It is a marine, deep water-dwelling eel which is known from the Gulf of Mexico to the Amazon, in the western Atlantic Ocean. It dwells at a depth range of 366–475 meters. Males can reach a maximum total length of 39.5 centimeters.
Blachea longicaudalis is an eel in the family Congridae. It was described by Emma Stanislavovna Karmovskaya in 2004. It is a marine, deep water-dwelling eel which is known from Fiji and New Caledonia, in the western Pacific Ocean. It dwells at a depth range of 400–461 metres. Males can reach a maximum total length of 68.3 centimetres, while females can reach a maximum TL of 57 cm.
Gnathophis neocaledoniensis is an eel in the family Congridae. It was described by Emma Stanislavovna Karmovskaya in 2004. It is a marine, deep water-dwelling eel which is known from New Caledonia, in the western Pacific Ocean. It dwells at a depth range of 520–580 metres. Males can reach a maximum total length of 18.5 centimetres.
Nettenchelys dionisi is an eel in the family Nettastomatidae. It was described by Alberto Brito in 1989. It is a marine, deep water-dwelling eel which is known from the Canary Islands, in the eastern central Atlantic Ocean. It dwells at a depth range of 350 to 400 metres, and leads a benthic lifestyle. Males can reach a maximum total length of 62 centimetres (24 in).
Nettenchelys erroriensis is an eel in the family Nettastomatidae. It was described by Emma Stanislavovna Karmovskaya in 1994. It is a marine, deep water-dwelling eel which is known from Error Seamount, in the western Indian Ocean. It dwells at a depth range of 395 to 420 metres. Females can reach a maximum total length of 33.5 centimetres (13.2 in).
Nettenchelys exoria is an eel in the family Nettastomatidae. It was described by James Erwin Böhlke and David G. Smith in 1981. It is a marine, deep water-dwelling eel which is known from the western central Atlantic Ocean, including Florida, USA and the Bahamas. It dwells at a depth range of 277 to 494 meters. Males can reach a maximum total length of 46.7 centimeters (18.4 in).
The bridge duckbill eel is an eel in the family Nettastomatidae. It was described by Peter Henry John Castle and David G. Smith in 1981. It is a marine, deep water-dwelling eel which is known from the western Pacific Ocean, including New Caledonia, the Philippines, and Indonesia. It dwells at a depth range of 400–412 metres (1,312–1,352 ft). Females can reach a maximum total length of 43.1 centimetres (17.0 in).
Nettenchelys inion is an eel in the family Nettastomatidae. It was described by David G. Smith and James Erwin Böhlke in 1981. It is a marine, deep water-dwelling eel which is known from a single specimen discovered near North Bimini Marine Protected Area in 1964. It is known to dwell at a depth range of 458 to 531 meters. Males can reach a total length of 42.3 centimeters (16.7 in).
Nettenchelys paxtoni is an eel in the family Nettastomatidae. It was described by Emma Stanislavovna Karmovskaya in 1999. It is a marine, tropical eel which is known from Vanuatu, in the western Pacific Ocean. The only known specimen had a total length of 24.8 centimetres (9.8 in), and was recovered from the stomach contents of a sea snake.
The pygmy pikeconger or pygmy duckbill eel, is an eel in the family Nettastomatidae. It was described by David G. Smith and James Erwin Böhlke in 1981. It is a marine, tropical eel which is known from the western central Atlantic Ocean, including Venezuela and the Gulf of Mexico, and possibly more locations. It is known to dwell at a depth range of 128 to 280 meters. Males can reach a maximum total length of 20.1 centimeters (7.9 in).
Nettenchelys taylori is an eel in the family Nettastomatidae. It was described by Alfred William Alcock in 1898. It is a marine, deep-water dwelling eel which is known from a single specimen from India, in the western Indian Ocean. From the specimen it is known to dwell at a depth of 786 metres (2,579 ft), and to reach a total length of 53.3 centimetres (21.0 in).
