The Atherinomorpha is a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

of fishes in the superorder

Acanthopterygii Acanthopterygii (meaning "spiny-finned one") is a superorder of teleost, bony fishes in the class Actinopterygii. Members of this superorder are sometimes called ray-finned fishes for the characteristic sharp, bony rays in their fins; however th ...

, the

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of sk ...

es, consisting of three

orders Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * H ...

. The clade is ranked as an infraseries within the subseries

Ovalentaria Ovalentaria is a clade of ray-finned fishes within the Percomorpha, referred to as a subseries. It is made up of a group of fish families which are referred to in ''Fishes of the World's'' fifth edition as'' incertae sedis'', as well as the order ...

, which in turn is ranked within the wider

Percomorpha Percomorpha () is an extremely large and diverse clade of ray-finned fish. With more than 17,000 known species (including Scombroidei, tuna, Syngnathiformes, seahorses, gobies, Cichlidae, cichlids, flatfish, Labridae, wrasse, Perciformes, perches ...

clade.

Characteristics

The species within the infraseries Atherinomorpha are generally small fishes which normally grow no longer than , although some

needlefish Needlefish (family Belonidae) or long toms are piscivorous fishes primarily associated with very shallow marine habitats or the surface of the open sea. Some genera include species found in marine, brackish, and freshwater environments (e.g., ...

es from the order

Beloniformes Beloniformes is an order composed of six families (and about 264 species) of freshwater and marine ray-finned fish: * Adrianichthyidae (ricefish and medakas) * Belonidae (needlefish) * Exocoetidae (flyingfishes) * Hemiramphidae (halfb ...

can grow as long as . The

testes A testicle or testis ( testes) is the gonad in all male bilaterians, including humans, and is homologous to the ovary in females. Its primary functions are the production of sperm and the secretion of androgens, primarily testosterone. The ...

of the males are of the restricted spermatogonial type, in which the testes change to reflect a seasonal pattern of reproduction. The females lay

demersal The demersal zone is the part of the sea or ocean (or deep lake) consisting of the part of the water column near to (and significantly affected by) the seabed and the benthos. The demersal zone is just above the benthic zone and forms a layer o ...

eggs with filaments on the

chorion The chorion is the outermost fetal membrane around the embryo in mammals, birds and reptiles (amniotes). It is also present around the embryo of other animals, like insects and molluscs. Structure In humans and other therian mammals, the cho ...

. They may or may not have spines in their fins but where these are present they are generally weak. The number of vertebrae is normally less than 24. The

pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral (belly) surface of fish, and are the lower of the only two sets of paired fins (the other being the laterally positioned pectoral fins). The pelvic fins are homologous to the hi ...

s are positioned abdominally, subabdominally, or thoracically and may be connected to the

pleural rib The pleural cavity, or pleural space (or sometimes intrapleural space), is the potential space between the pleurae of the pleural sac that surrounds each lung. A small amount of serous pleural fluid is maintained in the pleural cavity to enable ...

by a

ligament A ligament is a type of fibrous connective tissue in the body that connects bones to other bones. It also connects flight feathers to bones, in dinosaurs and birds. All 30,000 species of amniotes (land animals with internal bones) have liga ...

Ctenoid A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scales, which can also provide effective camouflage through the use of reflection and colouration, as w ...

scales may be present but this is rare within this grouping. The majority of the species within the Atherinomorpha are surface feeding fishes, and about three quarters of the species are restricted to fresh or brackish waters. Within this infraseries adaptation to

internal fertilisation Internal fertilization is the union of an egg and sperm cell during sexual reproduction inside the female body. Internal fertilization, unlike its counterpart, external fertilization, brings more control to the female with reproduction. For intern ...

has been independently evolved, especially in freshwater groupings, and this taxon contains a greater diversity of internal fertilization than any other group of fishes. Species may be oviparous or viviparous. The filaments on the chorion are used to stick to the substrate and in most taxa, other than the exocoetoids there is an obvious droplet of oil that forms at the

vegetal pole In developmental biology, an embryo is divided into two hemispheres: the animal pole and the vegetal pole within a blastula. The animal pole consists of small cells that divide rapidly, in contrast with the vegetal pole below it. In some cases, t ...

Taxonomy

There is very strong evidence that the Atherinomorpha forms a

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

grouping, supported by the emphasis of diverse and unusual reproductive adaptations and this has subsequently been supported by molecular studies. Within the group the

Atheriniformes The Atheriniformes, also known as the silversides, are an order of ray-finned fishes that includes the Old & New World silversides, the rainbowfishes, and several less-familiar families, including the unusual Phallostethidae. The order incl ...

are a sister group to the

and the

Cyprinodontiformes Cyprinodontiformes is an order (biology), order of Actinopterygii, ray-finned fish, comprising mostly small, freshwater fish. Many popular aquarium fish, such as killifish and Poeciliidae, live-bearers, are included. They are closely related t ...

, with the atherinids which have spines in their fins being regarded as the most basal members of the clade. The fossil range of the Atherinomorpha is the

Eocene The Eocene ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

to the present. The Atherinomorpha is classified as follows: * Infraseries Atherinomorpha ** Order

*** Suborder

Atherinopsoidei Atherinopsoidei is a suborder of the order Atheriniformes comprising two families, both of which are restricted to the Americas. Families The suborder contains the following families: * Family Atherinopsidae Fitzinger, 1873 (New World silversi ...

*** Suborder

Atherinoidei Atherinoidei is a suborder of the order Atheriniformes comprising six families, with a mainly Old World distribution, although a few species are found in the western Atlantic Ocean. Families The suborder contains the following families: * Famil ...

** Order

*** Suborder

Adrianichthyoidei The ricefishes are a family (biology), family (Adrianichthyidae) of small ray-finned fish that are found in fresh and brackish waters from India to Japan and out into the Malay Archipelago, most notably Sulawesi (where the Lake Poso and Lore Lin ...

*** Suborder

Exocoetoidei Exocoetoidei is a suborder of the order Beloniformes, which is sometimes known as the Belonoidei. It contains two superfamilies and five families. Classification Exocoetoidei is classified as follows: * Suborder Exocoetoidei ** Superfamily Sc ...

** Order

*** Suborder

Aplocheiloidei Aplocheiloidei is a suborder of the Order (biology), order Cyprinodontiformes consisting of three Family (biology), families which are commonly known as killifishes. Families The three families within the suborder Aplocheiloidei are: * Aplochei ...

*** Suborder

Cyprinodontoidei Cyprinodontoidei is a suborder of fishes, one of the two suborders in the order Cyprinodontiformes. The Cyprinodontoidei consists of eleven families which are found in the Americas, the Mediterranean and in Africa, including Madagascar. Classi ...

References

{{Taxonbar, From=Q254600 Ovalentaria