The Percopsiformes are a small order of freshwater

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 A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

es measuring less than 20 cm in length, comprising the

trout-perch ''Percopsis omiscomaycus'', also known as the trout-perch, the grounder or the sand minnow, is one of two species in the family Percopsidae. Its name comes from the Greek root words ''perc'', meaning perch and ''opsi'' meaning appearance. The spe ...

and its allies. It contains just ten

extant Extant or Least-concern species, least concern is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Exta ...

species, grouped into seven

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 three

families Family (from ) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictability, structure, and safety as ...

. Five of these genera are

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...

. They inhabit freshwater habitats in North America, and fossil evidence indicates that they have inhabited this region since the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

, with both suborders having diverged by the

Maastrichtian The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...

. Most species in this order are known from the eastern and central regions of North America, although the two ''Percopsis'' species have a primarily boreal and western distribution, with ''P. omiscomaycus'' reaching as far north as the

Arctic Circle The Arctic Circle is one of the two polar circles, and the northernmost of the five major circle of latitude, circles of latitude as shown on maps of Earth at about 66° 34' N. Its southern counterpart is the Antarctic Circle. The Arctic Circl ...

and ''P. transmontana'' being restricted to the

Pacific Northwest The Pacific Northwest (PNW; ) is a geographic region in Western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Though no official boundary exists, the most common ...

. They are generally small fish, ranging from in adult body length. They are grouped together because of technical characteristics of their internal anatomy, and the different species may appear quite different externally. Despite their scientific name and the common names for some taxa, they are not closely related to actual perches in the order

Perciformes Perciformes (), also called the Acanthopteri, is an order or superorder of ray-finned fish in the clade Percomorpha. ''Perciformes'' means " perch-like". Among the well-known members of this group are perches and darters ( Percidae), and als ...

, and rather represent a freshwater lineage of the otherwise almost entirely marine superorder

Paracanthopterygii Paracanthopterygii is a superorder of fishes. Members of this group are called paracanthopterygians. The oldest members are known as fossils from the Cenomanian. It includes five orders: * † Sphenocephaliformes * Percopsiformes ( trout-perche ...

. They are more closely related to the cods, dories, and the deep-sea tube-eye, and fossil evidence suggests that their closest relative was the extinct order Sphenocephaliformes, comprising two enigmatic genera of Late Cretaceous marine fish, as well as ''

Omosomopsis ''Omosomopsis'' is a genus of prehistoric ray-finned fish from the Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata f ...

'', another Cretaceous marine fish from

Morocco Morocco, officially the Kingdom of Morocco, is a country in the Maghreb region of North Africa. It has coastlines on the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to Algeria–Morocc ...

Classification

* Order Percopsiformes Berg 1937 ** Genus †'' Lateopisciculus'' Murray & Wilson 1996 ** Genus †'' Percopsiformorum'' tolith** Suborder Percopsoidei Berg 1937 *** Genus †'' Lindoeichthys'' (Late Cretaceous of Canada) *** Family

Percopsidae Percopsidae is a family of fish in the order Percopsiformes, with one extant genus with two species, both endemic to North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemi ...

Regan 1911 ">ercopsides Agassiz 1850; Erismatopteridae Jordan 1905 †Libotoniidae Grande, 1988**** Genus †'' Amphiplaga'' Cope 1877 **** Genus †''

Erismatopterus ''Erismatopterus'' is an extinct genus of percopsiform fish which lived during the early to middle Eocene epoch and containing the single species ''Erismatopterus levatus''. A report of the genus in sediments of similar age in Washington State h ...

'' Cope 1870 **** Genus †'' Libotonius'' Wilson 1977 **** Genus †'' Massamorichthys'' Murray 1996 **** Genus '' Percopsis'' Agassiz 1849 Columbia'' Eigenmann & Eigenmann 1892 non Rang 1834; ''Columatilla">Columbia_(fish).html" ;"title="'Columbia (fish)">Columbia'' Eigenmann & Eigenmann 1892 non Rang 1834; ''Columatilla'' Whitley 1940; ''Salmoperca'' Thompson 1850] ** Suborder Aphredoderoidei Berg 1937 [Amblyopsoidei Regan 1911; Aphredoderoidea; Amblyopsoidea] *** Family Aphredoderidae Bonaparte 1832 (Pirate perches) **** Genus †'' Trichophanes'' Cope 1872 **** Genus '' Aphredoderus'' Lesueur 1833 ex Cuvier & Valenciennes 1833 'Sternotremia'' Nelson 1876; ''Asternotremia">Sternotremia.html" ;"title="'Sternotremia">'Sternotremia'' Nelson 1876; ''Asternotremia'' Nelson ex Jordan 1877; ''Scolopsis'' Gilliams 1824 non Cuvier 1814] *** Family Amblyopsidae Bonaparte 1832 [Hypsaeidae Storer 1846] (Cavefishes) **** Genus ''Typhlichthys'' Girard 1859 (Southern cavefish) **** Genus '' Speoplatyrhinus'' Cooper & Kuehne 1974 (Alabama cavefish) **** Genus '' Forbesichthys'' Jordan 1929 'Forbesella'' Jordan & Evermann 1927 non Herdman 1891 non Lacaze-Duthiers & Delage 1892">Forbesella.html" ;"title="'Forbesella">'Forbesella'' Jordan & Evermann 1927 non Herdman 1891 non Lacaze-Duthiers & Delage 1892(Spring cavefish) **** Genus ''Chologaster'' Agassiz 1853 (Swampfish) **** Genus ''Amblyopsis'' de Kay 1842 [''Troglichthys'' Eigenmann 1899; ''Poecilosomus'' Swainson 1839]

References

{{Authority control Percopsiformes, Taxa named by Lev Berg Extant Campanian first appearances Ray-finned fish orders