Actinopterygii, members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species.
Osteichthyes, commonly referred to as the bony fish, is a diverse superclass of vertebrates that have skeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes, which have skeletons primarily composed of cartilage. The vast majority of fish are members of Osteichthyes, which is an extremely diverse and abundant group consisting of 45 orders, and over 435 families and 28,000 species. It is the largest class of vertebrates in existence today. The group Osteichthyes is divided into the ray-finned fish (Actinopterygii) and lobe-finned fish (Sarcopterygii). The oldest known fossils of bony fish are about 425 million years old, which are also transitional fossils, showing a tooth pattern that is in between the tooth rows of sharks and bony fishes.
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration. Scales are quite common and have evolved multiple times through convergent evolution, with varying structure and function.
Tetrapods are four-limbed vertebrate animals constituting the superclass Tetrapoda. It includes all extant and extinct amphibians, and the amniotes which in turn evolved into the sauropsids and synapsids. Some tetrapods such as snakes and legless lizards had evolved to become limbless via mutations of the Hox gene, although some do still have a pair of vestigial spurs that are remnants of the hindlimbs.
Lungfish are freshwater vertebrates belonging to the class Dipnoi. Lungfish are best known for retaining ancestral characteristics within the Osteichthyes, including the ability to breathe air, and ancestral structures within Sarcopterygii, including the presence of lobed fins with a well-developed internal skeleton. Lungfish represent the closest living relatives of the tetrapods. The mouths of lungfish typically bear tooth plates, which are used to crush hard shelled organisms.
Bichirs and the reedfish comprise Polypteridae, a family of archaic ray-finned fishes and the only family in the order Polypteriformes.
Fish anatomy is the study of the form or morphology of fish. It can be contrasted with fish physiology, which is the study of how the component parts of fish function together in the living fish. In practice, fish anatomy and fish physiology complement each other, the former dealing with the structure of a fish, its organs or component parts and how they are put together, such as might be observed on the dissecting table or under the microscope, and the latter dealing with how those components function together in living fish.
Acanthodii or acanthodians is an extinct class of gnathostomes. They are currently considered to represent a paraphyletic grade of various fish lineages basal to extant Chondrichthyes, which includes living sharks, rays, and chimaeras. Acanthodians possess a mosaic of features shared with both osteichthyans and chondrichthyans. In general body shape, they were similar to modern sharks, but their epidermis was covered with tiny rhomboid platelets like the scales of holosteians.
Enamelin is an enamel matrix protein (EMPs), that in humans is encoded by the ENAM gene. It is part of the non-amelogenins, which comprise 10% of the total enamel matrix proteins. It is one of the key proteins thought to be involved in amelogenesis. The formation of enamel's intricate architecture is thought to be rigorously controlled in ameloblasts through interactions of various organic matrix protein molecules that include: enamelin, amelogenin, ameloblastin, tuftelin, dentine sialophosphoprotein, and a variety of enzymes. Enamelin is the largest protein (~168kDa) in the enamel matrix of developing teeth and is the least abundant of total enamel matrix proteins. It is present predominantly at the growing enamel surface.
Tiktaalik is a monospecific genus of extinct sarcopterygian from the Late Devonian Period, about 375 Mya, having many features akin to those of tetrapods. Tiktaalik is estimated to have had a total length of 1.25–2.75 metres (4.1–9.0 ft) based on various specimens.
Holostei is a group of ray-finned bony fish. It is divided into two major clades, the Halecomorphi, represented by the single living genus, Amia with two species, the bowfins, as well as the Ginglymodi, the sole living representatives being the gars (Lepisosteidae), represented by seven living species in two genera. The earliest members of the clade appeared during the Early Triassic, over 250 million years ago.
Andreolepis is an extinct genus of prehistoric fish, which lived around 420 million years ago. It was described by Walter Gross in 1968 based on scales found in the Hemse Formation in Gotland, Sweden. It is placed in the monogeneric family Andreolepididae and is generally regarded as a primitive member of the class Actinopterygii based on its ganoid scale structure; however some new research regards it as a stem group of osteichthyans.
The barred bichir, armoured bichir, bandback bichir, or banded bichir is an elongated fish found in the Congo River, specifically in the upper and middle portions. This species is one of the more commonly available in commercial pet stores.
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 well as possible hydrodynamic advantages. The term scale derives from the Old French escale, meaning a shell pod or husk.
Enameloid, also known as durodentine or vitrodentine, is an enamel-like tissue found in many fish. It is the primary outer component of shark odontodes. Although the origin of enameloid is debated, it is probably homologous to dentine rather than true enamel, despite its enamel-like strength and development. The term covers any hyper-mineralized tissue with an organic "scaffold" consisting of ectodermal and ectomesenchymal proteins.
Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of Actinopterygii and Chondrichthyes fishes. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as seen in sharks. Apart from the tail or caudal fin, fish fins have no direct connection with the spine and are supported only by muscles. Their principal function is to help the fish swim.
The evolution of fish began about 530 million years ago during the Cambrian explosion. It was during this time that the early chordates developed the skull and the vertebral column, leading to the first craniates and vertebrates. The first fish lineages belong to the Agnatha, or jawless fish. Early examples include Haikouichthys. During the late Cambrian, eel-like jawless fish called the conodonts, and small mostly armoured fish known as ostracoderms, first appeared. Most jawless fish are now extinct; but the extant lampreys may approximate ancient pre-jawed fish. Lampreys belong to the Cyclostomata, which includes the extant hagfish, and this group may have split early on from other agnathans.
The evolution of tetrapods began about 400 million years ago in the Devonian Period with the earliest tetrapods evolved from lobe-finned fishes. Tetrapods are categorized as animals in the biological superclass Tetrapoda, which includes all living and extinct amphibians, reptiles, birds, and mammals. While most species today are terrestrial, little evidence supports the idea that any of the earliest tetrapods could move about on land, as their limbs could not have held their midsections off the ground and the known trackways do not indicate they dragged their bellies around. Presumably, the tracks were made by animals walking along the bottoms of shallow bodies of water. The specific aquatic ancestors of the tetrapods, and the process by which land colonization occurred, remain unclear. They are areas of active research and debate among palaeontologists at present.
Amia, commonly called bowfin, is a genus of bony fish related to gars in the infraclass Holostei. They are regarded as taxonomic relicts, being the sole surviving species of the order Amiiformes, which dates from the Jurassic to the Eocene, persisting to the present. There are two living species in Amia, Amia calva and Amia ocellicauda, and a number of extinct species which have been described from the fossil record.
Spiracles are openings on the surface of some animals, which usually lead to respiratory systems.
