Flounders are a group of flatfish species. They are demersal fish, found at the bottom of oceans around the world; some species will also enter estuaries.
A flatfish is a member of the ray-finned demersal fish order Pleuronectiformes, also called the Heterosomata, sometimes classified as a suborder of Perciformes. In many species, both eyes lie on one side of the head, one or the other migrating through or around the head during development. Some species face their left sides upward, some face their right sides upward, and others face either side upward.
Halibut is the common name for two flatfish in the genus Hippoglossus from the family of right-eye flounders and, in some regions, and less commonly, other species of large flatfish.
A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group. This is especially important where the descendant group is sharply differentiated by gross anatomy and mode of living from the ancestral group. These fossils serve as a reminder that taxonomic divisions are human constructs that have been imposed in hindsight on a continuum of variation. Because of the incompleteness of the fossil record, there is usually no way to know exactly how close a transitional fossil is to the point of divergence. Therefore, it cannot be assumed that transitional fossils are direct ancestors of more recent groups, though they are frequently used as models for such ancestors.
Sinistral and dextral, in some scientific fields, are the two types of chirality ("handedness") or relative direction. The terms are derived from the Latin words for "left" (sinister) and "right" (dexter). Other disciplines use different terms or simply use left and right.
The common dab is an edible flatfish of the family Pleuronectidae. It is a demersal fish native to shallow seas around Northern Europe, in particular the North Sea, where it lives on sandy bottoms down to depths of about 100 metres (330 ft). It can reach 40 centimetres (16 in) in length and can weigh up to 1 kilogram (2.2 lb), though most specimens grow no longer than 20 centimetres (7.9 in).
The California halibut or California flounder is a large-tooth flounder native to the waters of the Pacific Coast of North America from the Quillayute River in Washington to Magdalena Bay in Baja California. It feeds near shore and is free swimming. It typically weighs 6 to 30 pounds. It is much smaller than the larger and more northern-ranging Pacific halibut that can reach 300 pounds (140 kg).
Hypsidoris is an extinct genus of catfish, classified within its own family Hypsidoridae, from the Eocene epoch of North America.
Berycopsis is an extinct genus of beardfish from the Cretaceous period. Fossils are known from England.
Axestemys is an extinct genus of softshell turtle that lived from the Late Cretaceous to the Eocene in western North America and Europe.
The common sole, Dover sole, or black sole is a species of flatfish in the family Soleidae. It lives on the sandy or muddy seabed of the northern Atlantic and the Mediterranean Sea where it often semi-immerses itself in the substrate. The upper side is greyish-brown while the underside is white. It grows to a maximum length of about 70 cm (28 in). The species is prized as a food fish, being caught mostly by trawling on the seabed.
Amphistium paradoxum, the only species classified under the genus Amphistium, is a fossil fish which has been identified as a Paleogene relative of the flatfish, and as a transitional fossil. In a typical modern flatfish, the head is asymmetric with both eyes on one side of the head. In Amphistium, the transition from the typical symmetric head of a vertebrate is incomplete, with one eye placed near the top of the head.
Heteronectes chaneti is a fossil fish which has been identified as a primitive flatfish, dating to the early Eocene of France.
Joleaudichthys is an extinct genus of prehistoric flatfish that lived from the early to middle Eocene of Egypt.
The Pacific sand sole, also known as simply sand sole, is a flatfish species inhabiting the northeastern Pacific waters where it lives on sandy bottoms. The only species in the genus, Psettichthys, it ranges from the Bering Sea to Northern California.
The New Zealand brill, Colistium guntheri, is an edible flatfish of the family Pleuronectidae. It is a demersal fish native to shallow seas around New Zealand, at depths of between 27 metres (89 ft) and 49 metres (161 ft). It can grow to 91 centimetres (36 in) in length and can weigh up to 1.8 kilograms (4.0 lb).
Citharichthys gymnorhinus, the anglefin whiff, is a species of flatfish in the large-tooth flounder family Paralichthyidae. It is a demersal marine fish that inhabits the mid to outer continental shelf of the western Atlantic Ocean, in both tropical and subtropical waters. It ranges from the Bahamas and Florida in the north to Guyana and Nicaragua in the south, though larvae samples have also been collected off the coast of Canada. It occurs at depths between 35 and 200 metres, but is most commonly found in shallower waters.
The comb flounder is a flatfish of the family Pleuronectidae. It is a demersal fish that lives on saltwater bottoms at depths of between 20 and 406 metres. Its natural habitat is the tropical waters of the western Indian Ocean, from KwaZulu-Natal and Mozambique in Southern Africa, to coastal Tanzania and Kenya in the African Great lakes region, to Somalia in the Horn of Africa, to Karnataka and Maharashtra in India. It can grow up to 19 centimetres (7.5 in) in length.
Vision is an important sensory system for most species of fish. Fish eyes are similar to the eyes of terrestrial vertebrates like birds and mammals, but have a more spherical lens. Birds and mammals normally adjust focus by changing the shape of their lens, but fish normally adjust focus by moving the lens closer to or further from the retina. Fish retinas generally have both rod cells and cone cells, and most species have colour vision. Some fish can see ultraviolet and some are sensitive to polarised light.
Citharichthys cornutus, the horned whiff, is a species of flatfish in the large-tooth flounder family Paralichthyidae. This bathydemersal marine fish inhabits the continental shelves of the western Atlantic Ocean, in both tropical and subtropical waters. It ranges from New Jersey in the north to Uruguay in the south, though larvae samples have also been collected off the coast of Canada. It occurs at depths between 30 and 400 metres, though it is usually found in deeper waters.
