Actinopterygii

Gars ( Lepisosteus sp.) In Düsseldorf Aquazoo - Löbbecke Museum

The ray-finned fishes ( Actinopterygii ) are a class of bony fishes ( Osteichthyes ).

Except for the meat -finned fishes ( Sarcopterygii ) all bony fishes belong to this taxon, which adds up to nearly half of all vertebrate species.

The ray-finned fishes are found worldwide today and colonize all aquatic habitats from the deep sea (up to about -8400 feet ) to high mountains (up to 4,500 meters) and of thermal springs ( 43 ° C) up to the polar oceans (-1.8 ° C ). They are highly variable in morphological, ecological and behavioral biological terms.

• 5.1 Notes and references

Origin of the name

The scientific name " Actinopterygii " is combined from the Ancient Greek words ἀκτίς ( Aktís, beam ') and πτερύγιον ( pterýgion, wing ' or ' Fin '), that is equivalent to the German common name " ray-finned ". It refers to the typical anatomy of the fins ( see below).

Morphological characteristics

One of the characteristic features of ray-finned design and name for the taxon is the formation of paired fins (pectoral and pelvic fins ) in the form of so-called fin rays ( Actinopterygia, Sg Actinopterygium ). The sister group of ray-finned fishes, the flesh -finned fishes ( Sarcopterygii ), however, have so-called meat fins ( Sarcopterygia, Sg Sarcopterygium ). The vast majority of these rays fin consists of the bony fin rays ( radii, Sg radius ) and the webbing ( patagium ), which is spanned by the radii. The relatively long radii sitting on a comparatively short Flossenbasiskelett, with proximal ( close to the fuselage ) basals of distal ( distant from the fuselage ), rod-shaped radials are distinguished. In almost all extant ray-finned taxa, however, lack the basals. The muscles of the fin movement sit in all teleosts only on fin base skeleton. Accordingly, the entire fin base, ie fin base skeleton together with muscles in Strahlenflossern rather unimpressive. The Fleischflossern is the fin base, sometimes the unpaired fins, compared to the fin rays much longer and more strongly developed, so that a relatively large portion of the fin in the living animal is " meaty ".

The tooth crowns of actinopterygians distinguished not only by the coating of normal enamel ( Ganoin ) by an additional small cap or " wart " from Acrodin, a very hard, transparent, melting like substance on the top of the crown (apex) of.

The front of the two dorsal fins in the basic blueprint of bony fish lacks: This primarily single dorsal fin of the ray-finned fishes may also be secondarily divided into several fins.

The scales are connected by a hook system hinged together. They are original highly mineralized, that is, with a layer of Ganoin coated ( Ganoidschuppe ). This condition is widespread in the Paleozoic and Mesozoic fossil Strahlenflossern, but is found today only in sturgeon ( Acipenseridae ) and gars ( Lepisosteidae ). However, by far the most common type of shed with living today Strahlenflossern is the Elasmoidschuppe. In this the Ganoin is reduced to microscopic residues.

First appearance in the fossil record

The Lophosteiformes and Naxilepis fragmentary finds from the late Silurian ( about 420 mya ) of Europe and Siberia and China, once considered the oldest fossil remains of Strahlenflossern. Meanwhile classifies If these representatives, however, as a basal bony fishes. The oldest skeletal remains, which one can safely assign Strahlenflossern originate from the Middle Devonian ( about 380 mya ) from Europe and Canada ( Cheirolepis ). Other European skeletal remains from this period are Stegotrachelus, Moythomasia and Orvikuina.

System

The Strahlenflossern includes over 30,000 species, of which 15,150 are freshwater fish, 14,740 occur in the sea and 720 species live in both habitats and in brackish water.

The modern cladistic systematics differs significantly from the classical systematics.

Classical systematics

• Ray-finned fishes ( Actinopterygii ) Cladistia Order Flösselhechtartige ( Polypteriformes )

• Order Sturgeons ( Acipenseriformes )

• Order billfish behaved ( Semionotiformes )
• Order Bowfin behaved ( Amiiformes )
• Subclass of True bony fish ( Teleostei )

Modern systematics

• Ray-finned fishes ( Actinopterygii ) Flössler ( Polypteriformes )
• Actinopteri Sturgeons ( Acipenseriformes )
• Neuflosser ( Neopterygii ) Billfish behaved ( Lepisosteiformes )
• Halecostomi1 Bowfin behaved ( Amiiformes )
• True bony fish ( Teleostei )

1 Alternative to group the Bowfin -like along with the teleosts as Halecostomi exists the view that bowfin and gar -like -like a common taxon, the Holostei form, which then is a sister group to teleosts, and together with the latter Neopterygier.