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.
Scomber is a genus of fish in the family Scombridae living in the open ocean found in Atlantic, Indian and Pacific Ocean. The genus Scomber and the genus Rastrelliger comprise the tribe Scombrini, known as the "true mackerels". These fishes have an elongated body, highly streamlined, muscular and agile. The eyes are large, the head is elongated, with a big mouth provided with teeth. They have two triangular dorsal fins, with some stabilizing fins along the caudal peduncle. The basic color is blue-green with a silvery white belly and a darker back, usually black mottled.
Casierius is an extinct genus of marine ray-finned fish that lived during the Albian stage of the Early Cretaceous epoch. It was a relative of the modern bonefish in the extinct family Phyllodontidae, although some authorities consider it either a true albulid or a very early eel. It contains a single species, C. heckeli, known from the Glen Rose Formation near Hood County, Texas.
Atopocephala is an extinct genus of prehistoric freshwater ray-finned fish that lived during the Middle Triassic epoch. It contains a single species, A. watsoni from the Karoo Supergroup of South Africa. A potential indeterminate species was known from the Timezgadiouine Formation of Morocco, but is now considered an indeterminate actinopterygian.
Australosomus is an extinct genus of prehistoric ray-finned fish that lived during the Early Triassic epoch in what is now Greenland, Kenya, Tanzania, Madagascar, South Africa and Canada.
Laytonia is an extinct genus of prehistoric halosaur that lived in deep water off the North American Pacific Coast from the Zemorrian Epoch until during the Upper Miocene subepoch, when tectonic uplift effectively destroyed the genus' habitat by making the deep water too shallow.
Eophycis is an extinct genus of prehistoric morid gadiform fish that lived during the early Oligocene epoch in the Paratethys ocean in what now the Polish Carpathians.
Berycomorus is an extinct genus of prehistoric marine ray-finned fish that lived during the late Eocene epoch. It contains a single species, B. firdoussi, from the Pabdeh Formation of Iran.
Besania is an extinct genus of prehistoric marine ray-finned fish that lived during the Anisian and Ladinian ages of the Middle Triassic epoch in what is now southern/southeastern Switzerland and northern Italy. Fossils were recovered from the Besano Formation of Monte San Giorgio area and the Prosanto Formation of canton Graubünden, Switzerland.
Bregmacerina is an extinct genus of prehistoric marine ray-finned fish, most likely a codlet, that lived during the early part of the Miocene epoch. It contains a single species, B. antiqua, from the Burdigalian Sakaraul Horizon Formation of North Caucasus, Russia.
Acentrophorus is an extinct genus of prehistoric freshwater and marine ray-finned fish from the Roadian to the Wuchiapingian of England, Germany (Kupferschiefer), Italy and Russia. There may also be a Triassic occurrence in Australia.
Aluvarus praeimperialis is an extinct ray-finned fish, known from two headless fossil specimens found in the Pabdeh Formation, a Late Eocene stratum from the Priabonian epoch, of what is now Iran. A. praeimperialis was originally thought to be a luvar, described as "Luvarus praeimperialis", as it was thought to be a predecessor to the modern luvar. A later reexamination of the specimens showed that they were too incomplete to demonstrate such a conclusion and had no clear exclusive shared traits with luvar, and were renamed "Aluvarus", meaning "not luvar" or "different than luvar". However, some authorities still retain it as a luvar.
Anaethalion is an extinct genus of prehistoric marine and freshwater ray-finned fish related to modern tarpons and ladyfish. It is known from the Late Jurassic to the Early Cretaceous of Europe and northeasterrn Asia, roughly encompassing the Tethys Ocean.
Beaumontoperca is an extinct genus of freshwater or estuarine temperate bass known from Late Oligocene. It contains a single species, B. beaumonti, from the Niveau du gypse d'Aix Formation of Aix-en-Provence, France.
Caeus is an extinct genus of prehistoric marine ray-finned fish, closely related to the modern milkfish. It contains a single species, C. leopoldi from the Early Cretaceous of the Pietraroja Plattenkalk, Italy. It is one of the largest teleosts known from the Pietraroja formation, and is known by only a single specimen.
Hulettia is an extinct genus of ray-finned fish known from United States. This fish genus contains two species, H. americana and H. hawesi.
Palaeogadus is an extinct genus of prehistoric bony fish. It was a nektonic carnivore found in coastal and estuarine marine environments, with fossils found from the Oligocene to Miocene at sites in Denmark, Germany, Poland, Georgia, and Azerbaijan.
Bathyprion danae, the fangtooth smooth-head, is a species of slickhead found in deep waters of the Atlantic and Pacific Oceans. It is in the monotypic genus Bathyprion.
Chuhsiungichthys is an extinct genus of ichthyodectiform ray-finned fish that lived in freshwater environments in what is now Yunnan, China, and Kyushu, Japan during the Cretaceous. It differs from its sister genus, Mesoclupea, primarily by having a comparatively more anteriorly-placed dorsal fin.
Challaia is an extinct genus of prehistoric freshwater ray-finned fish that lived during the Triassic period in what is now Argentina (Mendoza). Two species are known, C. magna, most likely from the Cerro de Las Cabras Formation, and C. elongata from the Los Rastros Formation. Three other species, C. multidentata, C. striata and C.? cacheutensis, are considered nomina dubia.
