A leptocephalus 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 4 orders, 24 families, and 156 genera. This group is thought to have arisen in the Cretaceous period over 140 million years ago.
Eels are any of several long, thin, bony fishes of the order Anguilliformes. They have a catadromous life cycle, that is: at different stages of development migrating between inland waterways and the deep ocean. Because fishermen never caught anything they recognized as young eels, the life cycle of the eel was long a mystery. Of particular interest has been the search for the spawning grounds for the various species of eels, and identifying the population impacts of different stages of the life cycle.
Leptocephalus is a genus that was used for species of larval eels, called leptocephali. Leptocephali larvae differ so much in appearance from their adults. When first discovered, leptocephali were thought to be a distinct type of fish, not an eel specie. Because of this, the genus designation of Leptocephalus was used for a while for an unidentified leptocephali. After it was known that these were eel larvae, it was identified to be part of a wastebasket taxon, but not anymore in the present classification system. 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.
The Mediterranean moray, also known as Roman eel, is a species of fish in the moray eel family. It has a long eel-like body and is found in the eastern Atlantic Ocean and Mediterranean Sea. Its bite can be dangerous to humans.
The Colocongridae, the worm eels or short-tail eels, are a family of eels, containing a single genus, Coloconger.
Uropterygius macularius is a moray eel found in coral reefs in the western Atlantic Ocean. It is commonly known as the marbled moray.
The ridged eel is an eel in the family Moringuidae. It was described by Charles Frédéric Girard in 1858. It is a subtropical, marine eel known from the western Atlantic Ocean, including the northwestern Gulf of Mexico, Cuba, and northern South America. The larvae have been found ranging from the Straits of Florida to Brazil. It typically dwells at a depth range of 13–180 m, and inhabits offshore banks. Males can reach a maximum total length of 30 cm.
The swollengut worm eel is an eel in the family Moringuidae. It was described by Peter Henry John Castle in 1965, originally under the genus Leptocephalus. It is a marine, temperate water-dwelling eel endemic to Australia.
Coloconger cadenati is an eel in the family Colocongridae. It was described by Robert H. Kanazawa in 1961. It is a marine, deep-water dwelling eel which is known from Senegal to the Gulf of Guinea in the eastern Atlantic Ocean. It is known from a depth range of 270–600 m. Males can reach a maximum total length of 90 cm. The diet of C. cadenati consists primarily of benthic crustaceans.
Coloconger eximia is an eel in the family Colocongridae. It was described by Peter Henry John Castle in 1967, originally under the genus Ascomana. It is a marine, deep-water dwelling eel which is known from Cape Peninsula, South Africa, in the southeastern Atlantic Ocean.
Coloconger japonicus is a species of eels in the family Colocongridae. It was described by Yoshihiko Machida in 1984. It is a marine, deep-water dwelling eel which is known from the East China Sea. It dwells at a depth range of 750–760 metres. Males can reach a maximum total length of 56 centimetres.
Coloconger meadi is an eel in the family Colocongridae. It was described by Robert H. Kanazawa in 1957. It is a marine, deep-water dwelling eel from the Gulf of Mexico and Suriname in the western central Atlantic Ocean. It dwells at a depth range of 650–925 m. Males can reach a maximum total length of 37.7 cm.
The froghead eel is an eel in the family Colocongridae. It was described by Alfred William Alcock in 1889. It is a marine, deep-water dwelling eel which is known from the Indo-west Pacific, including East Africa, Madagascar, and southern Japan. It dwells at a depth range of 300–1134 metres. Males can reach a maximum total length of 50 centimetres.
The deepsea conger is an eel in the family Congridae. It was described by Peter Henry John Castle in 1960, originally under the genus Pseudoxenomystax. It is a marine, temperate water-dwelling eel which is known from the southwestern Pacific Ocean. It leads a benthic lifestyle and inhabits continental shelves and slopes. Males can reach a maximum total length of 100 centimetres.
Bathycongrus trilineatus is an eel in the family Congridae. It was described by Peter Henry John Castle in 1964, originally under the genus Leptocephalus. It is a tropical, marine eel which is known from the western central Pacific Ocean. It is known to dwell at a depth of 50 metres.
The Longnose conger is an eel in the family Congridae. It was described by Peter Henry John Castle in 1968, originally under the genus Congrina. It is a marine, deep water-dwelling eel which is known from the Indo-Western Pacific, including Mozambique, Natal, South Africa, Japan, the Philippines, and Indonesia. It dwells at a depth range of 250–500 metres. Males can reach a maximum total length of 55 centimetres.
Congriscus megastomus is an eel in the family Congridae. It was described by Albert Günther in 1877, originally under the genus Congromuraena. It is a marine, temperate-water dwelling eel which is known from Japan and the Kyushu–Palau Ridge, in the northwestern Pacific Ocean. It inhabits reefs. Males can reach a maximum total length of 40 centimeters. This species' remarkably large and distinct leptocephalus larvae were previously known under the name Thalassenchelys coheni. In 2016, scientists used genetic techniques to link the larvae to the adult C. megastomus. These larvae reach a maximum size of 30 cm (12 in) and have a number of unusual characteristics, including two forward-facing front teeth that may be used for feeding on different prey than other eel larvae.
Heteroconger tomberua is an eel in the family Congridae. It was described by Peter Henry John Castle and John Ernest Randall in 1995. It is a marine, tropical eel which is known from the western central Pacific Ocean, including Fiji and possibly New Caledonia, the Philippines, the Nicobar Islands, Papua New Guinea, and Sri Lanka. It is known to dwell at a depth of 36 m (118 ft). Males can reach a maximum total length of 42.8 cm.
The deepwater big-eyed worm eel is an eel in the family Ophichthidae. It was described by John E. McCosker in 2006. It is a subtropical, marine eel which is known from New Zealand, in the southwestern Pacific Ocean. It dwells at a depth range of 425–820 metres. Females can reach a maximum total length of 58 centimetres.
The Bean's sawtooth eel is an eel in the family Serrivomeridae. It was described by Theodore Gill and John Adam Ryder in 1883. It is a marine, deep water-dwelling eel which is known from throughout the Atlantic Ocean, the Indian Ocean, and the Western Pacific Ocean, including Iceland, South Africa, Réunion, and Australia. It dwells at a depth range of 0–5,998 metres (0–19,680 ft), and leads a solitary lifestyle. It migrates vertically at night. Males can reach a maximum total length of 78-80 centimetres, making it the largest sawtooth eel.
