The true soles are a family, Soleidae, of

flatfish A flatfish is a member of the Ray-finned fish, ray-finned demersal fish Order (biology), suborder Pleuronectoidei, also called the Heterosomata. In many species, both eyes lie on one side of the head, one or the other migrating through or around ...

es. It includes saltwater and

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...

water species in the East Atlantic, Indian Ocean, West and Central Pacific Ocean, and the mediterranean sea. Freshwater species are found in Africa, southern Asia,

New Guinea New Guinea (; Hiri Motu: ''Niu Gini''; , fossilized , also known as Papua or historically ) is the List of islands by area, world's second-largest island, with an area of . Located in Melanesia in the southwestern Pacific Ocean, the island is ...

, and Australia. In the past, soles of the Americas (both fresh and salt water) were included in this family, but they have been separated to their own family, the American soles (Achiridae). The only true sole remaining in that region is '' Aseraggodes herrei'' of the Galápagos and

Cocos Island Cocos Island () is a volcanic island in the Pacific Ocean administered by Costa Rica, approximately southwest of the Costa Rican mainland. It constitutes the 11th of the 15 districts of Puntarenas Canton of the Puntarenas Province, Province of ...

. The true soles are bottom-dwelling fishes feeding on small

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s and other

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

s. The family contains 30

genera Genus (; : genera ) is a taxonomic rank above species and below family as used in the biological classification of living and fossil organisms as well as viruses. In binomial nomenclature, the genus name forms the first part of the binomial s ...

and a total of about 180 species. Soles begin life as bilaterally symmetric

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

e, with an eye on each side of the head, but during development, the left eye moves around onto the right side of the head. Adult soles lie on their left (blind) sides on the

sea floor The seabed (also known as the seafloor, sea floor, ocean floor, and ocean bottom) is the bottom of the ocean. All floors of the ocean are known as seabeds. The structure of the seabed of the global ocean is governed by plate tectonics. Most of ...

, often covered in mud, which in combination with their dark colours, makes them hard to spot. A flatfish resembling a small

halibut Halibut is the common name for three species of flatfish in the family of right-eye flounders. In some regions, and less commonly, other species of large flatfish are also referred to as halibut. The word is derived from ''haly'' (holy) and ...

or sole was observed by the bathyscaphe ''Trieste'' at the bottom of the

Mariana Trench The Mariana Trench is an oceanic trench located in the western Pacific Ocean, about east of the Mariana Islands; it is the deep sea, deepest oceanic trench on Earth. It is crescent-shaped and measures about in length and in width. The maxi ...

at a depth around . This observation has been questioned by fish experts, and recent authorities do not recognize it as valid.Jamieson, A.J., and Yancey, P. H. (2012).
On the Validity of the Trieste Flatfish: Dispelling the Myth.
'

The Biological Bulletin ''The Biological Bulletin'' is a peer review, peer-reviewed scientific journal covering the field of biology. The journal was established in 1897 as the ''Zoological Bulletin'' by Charles Otis Whitman and William Morton Wheeler. In 1899 the title ...

222(3): 171–175 Many soles are important food species: the

common sole The common sole, Dover sole, or black sole (''Solea solea'') is a species of flatfish in the family Soleidae. It is one of the largest fish in the '' Solea'' genus. It lives on the sandy or muddy seabed of the northern Atlantic and the Mediter ...

, ''Solea solea'', is popular in northern

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

and the

Mediterranean The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern ...

. The earliest known fossil remains of soles are indeterminate otoliths from 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 ...

-aged

London Clay The London Clay Formation is a Sediment#Shores and shallow seas, marine formation (geology), geological formation of Ypresian (early Eocene Epoch, c. 54-50 million years ago) age which outcrop, crops out in the southeast of England. The London C ...

. During the Middle Eocene (

Lutetian The Lutetian is, in the geologic timescale, a stage (stratigraphy), stage or age (geology), age in the Eocene. It spans the time between . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it ...

), the first fossil skeletons of soles are known in '' Eobuglossus'' and '' Turahbuglossus'' from Egypt. Image:Aesopia cornuta.jpg, Unicorn sole, ''Aesopia cornuta'' Image:Buglossidium luteum.jpg, Solenette, ''Buglossidium luteum'' Image:Solea solea 1.jpg,

Common sole The common sole, Dover sole, or black sole (''Solea solea'') is a species of flatfish in the family Soleidae. It is one of the largest fish in the '' Solea'' genus. It lives on the sandy or muddy seabed of the northern Atlantic and the Mediter ...

, ''Solea solea''

References

{{Authority control Carangiformes families Taxa named by Charles Lucien Bonaparte Extant Ypresian first appearances