Slickheads, also known as nakedheads or smoothheads, are deep water fishes that belong to the family Alepocephalidae. They are most commonly found in the bathypelagic layer, which is approximately 3000m below the surface. They get their name from the lack of scales on their heads. Similarly, the scientific name is from the Greek ᾰ̓- (''a''-, "not"); λέπος (''lepos'', "scale"); and κεφαλή (''kephalē'', "head"). It has about 22 genera with ca. 96 species. The only known fossil genus is '' Carpathichthys'' from the

Early Oligocene The Rupelian is, in the geologic timescale, the older of two age (geology), ages or the lower of two stage (stratigraphy), stages of the Oligocene epoch (geology), Epoch/series (stratigraphy), Series. It spans the time between . It is preceded b ...

of Poland, although an undescribed species of ''

Bathyprion ''Bathyprion'', is a genus of deepwater Marine life, marine Actinopterygii, ray-finned fish belonging to the Family (biology), family Alepocephalidae, the slickheads. Its only extant species is ''Bathyprion danae'', the fangtooth smooth-head. Thi ...

'' and several indeterminate taxa are also known from the same formation. Fossil

otoliths An otolith (, ' ear + , ', a stone), also called otoconium, statolith, or statoconium, is a calcium carbonate structure in the saccule or utricle of the inner ear, specifically in the vestibular system of vertebrates. The saccule and utricle, i ...

are also known, dating to the

Early Eocene In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...

Genera

Alepocephalidae contains the following extant genera: * '' Alepocephalus'' Risso, 1820 * ''

Asquamiceps ''Asquamiceps'' is a genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV cl ...

'' Zugmayer, 1911 * ''

Aulastomatomorpha ''Aulastomatomorpha'' is a monospecific genus of deepwater maine ray-finned fish belonging to the family Alepocephalidae, the slickheads. The only species in the genus is ''Aulastomatomorpha phospherops'', the luminous slickhead, which is found in ...

'' Alcock, 1890 * ''

Bajacalifornia ''Bajacalifornia'' is a genus of slickheads. It was described in 1925 by Charles Haskins Townsend and John Treadwell Nichols on the basis of ''Bajacalifornia burragei''Deep sea fishes of the ''Albatross'' Lower California Expedition. Bulletin o ...

'' Townsend & Nichols, 1925 * ''

Bathylaco ''Bathylaco'' is a genus of slickheads found in deep oceanic waters. It is one of nineteen genera in the family Alepocephalidae. Species There are currently three recognized species A species () is often defined as the largest group of or ...

'' Goode & T. H. Bean, 1896 * ''

Marshall Marshall may refer to: Places Australia *Marshall, Victoria, a suburb of Geelong, Victoria ** Marshall railway station Canada * Marshall, Saskatchewan * The Marshall, a mountain in British Columbia Liberia * Marshall, Liberia Marshall Is ...

, 1966 * ''

Bathytroctes ''Bathytroctes'' is a genus of deepwater marine ray-finned fishes belonging to the family Alepocephalidae Slickheads, also known as nakedheads or smoothheads, are deep water fishes that belong to the family Alepocephalidae. They are most com ...

'' Günther, 1878 * ''

Conocara ''Conocara'' is a genus of deepwater marine ray-finned fishes belonging to the family Alepocephalidae, the smooth-heads. These fishes are found in the deeper waters of the Oceans around the world. The generic name derives from Latin ''conicus' ...

'' Goode & T. H. Bean, 1896 * ''

Einara ''Einara'' is a small genus of slickheads found in the deep waters of the oceans. They can grow to standard length The etymology of the genus name is uncertain but could refer Norwegian marine biologist Einar Koefoed. Species There are curre ...

'' Parr, 1951 * ''

Herwigia ''Herwigia'' is a monospecific genus of deepwater maine ray-finned fish belonging to the family Alepocephalidae, the slickheads. The only species in the genus is ''Herwigia kreffti'', or Krefft's smooth-head, a species A species () is often ...

'' Nielsen, 1972 * ''

Leptochilichthys ''Leptochilichthys'' is a genus of fishes containing four species. ''Leptochilichthys'' is the only genus in the former family Leptochilichthyidae but is now included within the broader family Alepocephalidae.R. Betancur-Rodriguez, E. Wiley, N. ...

'' Garman, 1899 * ''

Leptoderma ''Leptoderma'' is a genus of slickheads found in the deep waters of the ocean The ocean is the body of salt water that covers approximately 70.8% of Earth. The ocean is conventionally divided into large bodies of water, which are also ref ...

'' Vaillant, 1886 * '' Microphotolepis'' Sazonov & Parin, 1977 * '' Mirognathus'' Parr, 1951 * '' Narcetes'' Alcock, 1890 * '' Photostylus'' Beebe, 1933 * '' Rinoctes'' Parr, 1952 * ''

Rouleina ''Rouleina'' is a genus of slickheads. The genus is named for the ichthyologist Louis Roule. Species There are currently 10 recognized species in this genus: * '' Rouleina attrita'' ( Vaillant, 1888) (Softskin smooth-head) * '' Rouleina danae' ...

'' D. S. Jordan, 1923 * '' Talismania'' Goode & T. H. Bean, 1896 * '' Xenodermichthys'' Günther, 1878

Description

The following characteristics are generally shared by the Alepocephalidae family: Their mouths consist of 80 to 100 razor-sharp teeth, being rather small and feeble. They are shaped in an eel-like elongation, with large eyes, gill rakers that range from moderate to long and numerous, and spineless fins. The single dorsal fin is located posterior to the midpoint of the body and there is no adipose dorsal fin present, there is a pectoral fin ranging from small to rudimentary located below the mid-flank, 4–18 rays, if pelvic fins are present, they exist in the abdominal region, with the origin being before the origin of the dorsal fin, they have forked caudal fins, and a tube above the base of pectoral fin that connects to a luminous gland on the shoulder girdle. They have no swim bladder. Some species bear

photophore A photophore is a specialized anatomical structure found in a variety of organisms that emits light through the process of boluminescence. This light may be produced endogenously by the organism itself (symbiotic) or generated through a mut ...

s. Their early life development is from large eggs directly into yolk sac juveniles that travel in deep waters. The largest species is the Yokozuna slickhead, ''Narcetes shonanmaruae'', which is also the largest completely bathyal

teleost Teleostei (; Ancient Greek, Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts (), is, by far, the largest group of ray-finned fishes (class Actinopterygii), with 96% of all neontology, extant species of f ...

fish.

Behaviour

It’s been thought that as the Alepocephalidae age, they move down layers in the ocean, (mesopelagic waters and bathypelagic waters) due to mostly adolescent Alepocephalidae being reported near the surface, although there have been sightings of juveniles only several meters above the sea floor, which could suggest that some species may travel between different depths throughout their life stages, a vertical shift. Vertical shift could occur due to predation being higher close to the sea floor and/or warmer water having a larger abundance of plankton. Juvenile slickheads may have a preference to travel upwards to take advantage of the lack of predation and abundance of food to increase survival rates.

Distribution

The species of Alepocephalidae are widely distributed throughout the world and can be found in the Atlantic, Indian, and western Pacific oceans, although they are difficult to find as they typically live around the bathypelagic layer of the ocean.

References

* R. Betancur-Rodriguez, E. Wiley, N. Bailly, A. Acero, M. Miya, G. Lecointre, G. Ortí
''Phylogenetic Classification of Bony Fishes – Version 4''
(2016) * * * Tony Ayling & Geoffrey Cox, ''Collins Guide to the Sea Fishes of New Zealand'', (William Collins Publishers Ltd, Auckland, New Zealand 1982) * Byrkjedal, I., Poulsen, J.Y., & Galbraith, J. (2011). "''Leptodermua macrophthalmum'' n.sp., a new species of smooth-head (Otocephala: Alepocephalidae) from the Mid Atlantic Ridge." ''Zootaxa'' 2876: 49–56.

External links

Otocephala families Taxa named by Charles Lucien Bonaparte {{Alepocephaliformes-stub