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44-525: Fossil taxa, see text 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

88-551: A distinct grade of organization—i.e. a 'level of complexity', measured in terms of how differentiated their organ systems are into distinct regions or sub-organs—with a distinct type of construction, which is to say a particular layout of organ systems. This said, the composition of each class is ultimately determined by the subjective judgment of taxonomists . In the first edition of his Systema Naturae (1735), Carl Linnaeus divided all three of his kingdoms of nature ( minerals , plants , and animals ) into classes. Only in

132-424: A distinct rank of biological classification having its own distinctive name – and not just called a top-level genus (genus summum) – was first introduced by French botanist Joseph Pitton de Tournefort in the classification of plants that appeared in his Eléments de botanique of 1694. Insofar as a general definition of a class is available, it has historically been conceived as embracing taxa that combine

176-468: A fan-shaped occlusion surface. These odontodes then wear to form a uniform crushing surface. In several groups, including the modern lepidosireniformes , these ridges have been modified to form occluding blades. The modern lungfishes have a number of larval features, which suggest paedomorphosis . They also demonstrate the largest genome among the vertebrates. Modern lungfish all have an elongate body with fleshy, paired pectoral and pelvic fins and

220-444: A layer of dried mucus . It can reach a length of up to 130 cm. The relationship of lungfishes to the rest of the bony fish is well understood: Recent molecular genetic analyses strongly support a sister relationship of lungfishes and tetrapods ( Rhipidistia ), with coelacanths branching slightly earlier. The relationships among lungfishes are significantly more difficult to resolve. While Devonian lungfish had enough bone in

264-541: A more appealing name due to their dragon-like appearance. Though predatory, they are otherwise peaceful, preferring to lie on the bottom (they tend to swim when there are lots of large plants present), and make good tankmates with other species large enough to not be prey but small enough to not eat them. Some aquarists note that pleco catfish eat the slime coat off of polypterids. Polypterids in captivity have life expectancies of 10–30+ years. They do well in heavily planted tanks as it mimics their natural habitat. In addition to

308-403: A pair of slit-like spiracles on the top of their heads that are used to breathe air, two gular plates, and paired ventral lungs . Both lungs are unchambered sacs. The larger right lung reaches the whole length of the body cavity, while the smaller left lung extends to the stomach. A slit-like opening called the glottis located on the ventral side of the oesophagus leads to the right lung, and

352-468: A pale grey belly. The west African lungfish , Protopterus annectens , is a species of lungfish found in West Africa. It has a prominent snout and small eyes . Its body is long and eel-like , some 9–15 times the length of the head. It has two pairs of long, filamentous fins . The pectoral fins have a basal fringe and are about three times the head length, while its pelvic fins are about twice

396-518: A separate opening on the right lung leads to the left lung. Four pairs of gill arches are present. Polypterids have a maximum body length ranging from 25 cm (9.8 in) to over 100 cm (39 in) depending on specific species and morphology. Polypterids are nocturnal and feed on small vertebrates, crustaceans, and insects. Their common aquarium diet includes bloodworms ( Chironomidae larvae). Polypterids are known to have extraordinary olfactory ability. Polypterid reproduction consists of

440-409: A significant reduction in the marginal bones and a cartilaginous braincase. The bones of the skull roof in primitive lungfish are covered in a mineralized tissue called cosmine , but in post- Devonian lungfishes, the skull roof lies beneath the skin and the cosmine covering is lost. All modern lungfish show significant reductions and fusions of the bones of the skull roof, and the specific bones of

484-440: A single unpaired caudal fin replacing the dorsal , caudal and anal fins of most fishes. Lungfish have a highly specialized respiratory system . They have a distinct feature in that their lungs are connected to the larynx and pharynx without a trachea. While other species of fish can breathe air using modified, vascularized gas bladders , these bladders are usually simple sacs, devoid of complex internal structure. In contrast,

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528-419: A taxonomy of the flowering plants up to the level of orders, many sources have preferred to treat ranks higher than orders as informal clades . Where formal ranks have been assigned, the ranks have been reduced to a very much lower level, e.g. class Equisitopsida for the land plants, with the major divisions within the class assigned to subclasses and superorders. The class was considered the highest level of

572-440: A true stomach . African and South American lungfish are capable of surviving seasonal drying out of their habitats by burrowing into mud and estivating throughout the dry season. Changes in physiology allow it to slow its metabolism to as little as one sixtieth of the normal metabolic rate, and protein waste is converted from ammonia to less-toxic urea (normally, lungfish excrete nitrogenous waste as ammonia directly into

616-466: Is a marked difference from most fish, whose fins usually have at least four bones at their base; and a marked similarity with nearly all land-dwelling vertebrates. They have the lowest aquatic respiration of all extant lungfish species, and their gills are greatly reduced and essentially non-functional in the adults. The marbled lungfish , Protopterus aethiopicus , is found in Africa. The marbled lungfish

660-716: Is brought to the lungs by paired pulmonary arteries, which branch from the fourth efferent branchial arteries (artery from the fourth gill arch), and oxygenated blood leaves the lungs in pulmonary veins. Unlike most lungfish and tetrapods , their lungs are smooth sacs instead of alveolated tissue. Polypterids are unique in that they breathe using recoil aspiration. Polypterids appear to prefer breathing air via their spiracles when undisturbed or in extremely shallow waters where they are unable to incline their body enough to breathe air through their mouth. Polypterids are popular subjects of public and large hobby aquaria . They are sometimes called dragon bichir or dragon fin in pet shops for

704-500: Is smooth, elongated, and cylindrical with deeply embedded scales . The tail is very long and tapers at the end. They are the largest of the African lungfish species as they can reach a length of up to 200 cm. The pectoral and pelvic fins are also very long and thin, almost spaghetti-like. The newly hatched young have branched external gills much like those of newts. After 2 to 3 months the young transform (called metamorphosis ) into

748-497: Is still used in respiration; deoxygenated blood loses some of its carbon dioxide as it passes through the gill before reaching the lung. This is because carbon dioxide is more soluble in water. Air flow through the mouth is tidal, and through the lungs it is bidirectional and observes "uniform pool" diffusion of oxygen. Lungfish are omnivorous , feeding on fish, insects , crustaceans , worms , mollusks , amphibians and plant matter. They have an intestinal spiral valve rather than

792-506: The Australian lungfish can breathe through its gills without needing air from its lung. In other species, the gills are too atrophied to allow for adequate gas exchange. When a lungfish is obtaining oxygen from its gills, its circulatory system is configured similarly to the common fish. The spiral valve of the conus arteriosus is open, the bypass arterioles of the third and fourth gill arches (which do not actually have gills) are shut,

836-571: The Scanilepiformes , are known from the later Permian to the Triassic , and are likely ancestral to polypterids. The oldest polypterids are around 100 million years old, from the early Late Cretaceous of South America and Africa. Polypterids are elongated fish with a unique series of dorsal finlets which vary in number from seven to 18, instead of a single dorsal fin . Each of the dorsal finlets has bifid (double-edged) tips, and are

880-453: The cranium ) and powerful adductor jaw muscles with the extant lungfish (Dipnoi). Like the African lungfishes , this species has an elongate, almost eel-like body. It may reach a length of 125 centimetres (4 ft 1 in). The pectoral fins are thin and threadlike, while the pelvic fins are somewhat larger, and set far back. The fins are connected to the shoulder by a single bone, which

924-497: The protist Polychaos dubium and the flowering plant Paris japonica at 670 billion and 150 billion, respectively. The gilled lungfish , Protopterus amphibius is a species of lungfish found in East Africa . It generally reaches only 44 centimetres (17 inches) long, making it the smallest extant lungfish in the world. This lungfish is uniform blue, or slate grey in colour. It has small or inconspicuous black spots, and

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968-578: The tetrapods (which includes living amphibians, reptiles, birds and mammals). The mouths of lungfish typically bear tooth plates, which are used to crush hard shelled organisms . Today there are only six known species of lungfish, living in Africa , South America , and Australia , though they were formerly globally distributed. The fossil record of the group extends into the Early Devonian , over 410 million years ago. The earliest known members of

1012-526: The Americas. Relatively little is known about the South American lungfish, or scaly salamander-fish . When immature it is spotted with gold on a black background. In the adult this fades to a brown or gray color. Its tooth-bearing premaxillary and maxillary bones are fused like other lungfish. South American lungfishes also share an autostylic jaw suspension (where the palatoquadrate is fused to

1056-669: The Late Carboniferous and the Jurassic . Lungfish remained present in the northern Laurasian landmasses into the Cretaceous period. The Queensland lungfish , Neoceratodus forsteri , is endemic to Australia. Fossil records of this group date back 380 million years, around the time when the higher vertebrate classes were beginning to evolve. Fossils of lungfish belonging to the genus Neoceratodus have been uncovered in northern New South Wales , indicating that

1100-652: The Queensland lungfish has existed in Australia for at least 100 million years, making it a living fossil and one of the oldest living vertebrate genera on the planet. It is the most primitive surviving member of the ancient air-breathing lungfish (Dipnoi) lineages. The five other freshwater lungfish species, four in Africa and one in South America, are very different morphologically to N. forsteri . The Queensland lungfish can live for several days out of

1144-458: The adult form, losing the external gills for gill openings. These fish have a yellowish gray or pinkish toned ground color with dark slate-gray splotches, creating a marbling or leopard effect over the body and fins. The color pattern is darker along the top and lighter below. The marbled lungfish's genome contains 133 billion base pairs , making it the largest known genome of any vertebrate . The only organisms known to have more base pairs are

1188-675: The ancestor of the extant coelacanths diverging a little earlier from a sarcopterygian progenitor. Youngolepis and Diabolepis , dating to 419–417 million years ago, during Early Devonian ( Lochkovian ), are the currently oldest known lungfish, and show that the lungfishes had adapted to a diet including hard-shelled prey ( durophagy ) very early in their evolution. The earliest lungfish were marine. Almost all post- Carboniferous lungfish inhabit or inhabited freshwater environments. There were likely at least two transitions amongst lungfish from marine to freshwater habitats. The last common ancestor of all living lungfish likely lived sometime between

1232-460: The animal kingdom are Linnaeus's classes similar to the classes used today; his classes and orders of plants were never intended to represent natural groups, but rather to provide a convenient "artificial key" according to his Systema Sexuale , largely based on the arrangement of flowers. In botany, classes are now rarely discussed. Since the first publication of the APG system in 1998, which proposed

1276-665: The body and fins except on its belly. They reach a length of about 100 cm in the wild. The spotted lungfish , Protopterus dolloi , is a species of lungfish found in Africa. Specifically, it is found in the Kouilou-Niari Basin of the Republic of the Congo and Ogowe River basin in Gabon . It is also found in the lower and Middle Congo River Basins . Protopterus dolloi can aestivate on land by surrounding itself in

1320-416: The female laying anywhere from 100 to 300 eggs over the span of a few days, and subsequent fertilization by the male. Polypterids possess paired lungs which connect to the esophagus via a glottis . They are facultative air-breathers, accessing surface air to breathe when the water they inhabit is poorly oxygenated. Their lungs are highly vascularized to facilitate gas exchange. Deoxygenated arterial blood

1364-558: The group were marine, while almost all post- Carboniferous representatives inhabit freshwater environments. Modern Latin from the Greek δίπνοος (dipnoos) with two breathing structures, from δι- twice and πνοή breathing, breath. All lungfish demonstrate an uninterrupted cartilaginous notochord and an extensively developed palatal dentition. Basal (" primitive ") lungfish groups may retain marginal teeth and an ossified braincase, but derived lungfish groups, including all modern species, show

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1408-449: The head length. In general, three external gills are inserted posterior to the gill slits and above the pectoral fins. It has cycloid scales embedded in the skin. There are 40–50 scales between the operculum and the anus and 36–40 around the body before the origin of the dorsal fin . It has 34–37 pairs of ribs . The dorsal side is olive or brown in color and the ventral side is lighter, with great blackish or brownish spots on

1452-491: The lungs of lungfish are subdivided into numerous smaller air sacs, maximizing the surface area available for gas exchange . Most extant lungfish species have two lungs, with the exception of the Australian lungfish, which has only one. The lungs of lungfish are homologous to the lungs of tetrapods. As in tetrapods and bichirs , the lungs extend from the ventral surface of the esophagus and gut. Of extant lungfish, only

1496-509: The oldest lungfish, and probably the oldest aquarium fish in the world is " Methuselah ", an Australian lungfish 4 feet (1.2 m) long and weighing around 40 pounds (18 kg). Methuselah is believed to be female, unlike its namesake , and is estimated to be over 90 years old. About 420 million years ago, during the Devonian , the last common ancestor of both lungfish and the tetrapods split into two separate evolutionary lineages, with

1540-563: The only family in the order Polypteriformes / p ə ˈ l ɪ p t ə r ɪ f ɔːr m iː z / . All the species occur in freshwater habitats in tropical Africa and the Nile River system, mainly swampy, shallow floodplains and estuaries . Cladistia , polypterids and their fossil relatives, are considered the sister group to all other extant ray-finned fishes ( Actinopteri ). They likely diverged from Actinopteri at least 330 million years ago. A closely related group,

1584-410: The only fins with spines; the rest of the fins are composed of soft rays. The body is covered in thick, bonelike, and rhombic ( ganoid ) scales. Their jaw structure more closely resembles that of the tetrapods than that of the teleost fishes. Bichirs have a number of other primitive characteristics, including fleshy pectoral fins superficially similar to those of lobe-finned fishes . They also have

1628-436: The second, fifth and sixth gill arch arterioles are open, the ductus arteriosus branching off the sixth arteriole is open, and the pulmonary arteries are closed. As the water passes through the gills, the lungfish uses a buccal pump. Flow through the mouth and gills is unidirectional. Blood flow through the secondary lamellae is countercurrent to the water, maintaining a more constant concentration gradient. When breathing air,

1672-473: The skull roof show no homology to the skull roof bones of ray-finned fishes or tetrapods . During the breeding season, the South American lungfish develops a pair of feathery appendages that are actually highly modified pelvic fins. These fins are thought to improve gas exchange around the fish's eggs in its nest. Through convergent evolution , lungfishes have evolved internal nostrils similar to

1716-758: The skull to determine relationships, post-Devonian lungfish are represented entirely by skull roofs and teeth, as the rest of the skull is cartilaginous . Additionally, many of the taxa already identified may not be monophyletic . Phylogeny after Kemp, Cavin & Guinot, 2017 † Diabolepis † Westollrhynchus † Ichnomylax † Dipnorhynchus † Speonesydrion † Uranolophus † Stomiahykus † Iowadipterus † Jessenia † Melanognathus † Tarachomylax † Dipterus † Adololopas † Chirodipterus australis † Gogodipterus † Pillararhynchus † Sorbitorhynchus † Chirodipterus liangchengi † Chirodipterus wildungensis † Sinodipterus Class (biology) The class as

1760-407: The spiral valve of the conus arteriosus closes (minimizing the mixing of oxygenated and deoxygenated blood), the third and fourth gill arches open, the second and fifth gill arches close (minimizing the possible loss of the oxygen obtained in the lungs through the gills), the sixth arteriole's ductus arteriosus is closed, and the pulmonary arteries open. Importantly, during air breathing, the sixth gill

1804-415: The taxonomic hierarchy until George Cuvier 's embranchements , first called Phyla by Ernst Haeckel , were introduced in the early nineteenth century. Bichir Erpetoichthys Polypterus See text for species. Bichirs / ˈ b ɪ ʃ ɪər z / and the reedfish comprise Polypteridae / p ɒ l ɪ p ˈ t ɛ r ɪ d iː / , a family of archaic ray-finned fishes and

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1848-470: The tetrapods' choana , and a brain with certain similarities to Lissamphibian brain (except for the Queensland lungfish, which branched off in its own direction about 277 million years ago and has a brain resembling that of the Latimeria ). The dentition of lungfish is different from that of any other vertebrate group. " Odontodes " on the palate and lower jaws develop in a series of rows to form

1892-457: The water if it is kept moist, but will not survive total water depletion, unlike its African counterparts. The South American lungfish , Lepidosiren paradoxa , is the single species of lungfish found in swamps and slow-moving waters of the Amazon , Paraguay , and lower Paraná River basins in South America. Notable as an obligate air-breather, it is the sole member of its family native to

1936-676: The water). Burrowing is seen in at least one group of fossil lungfish, the Gnathorhizidae . Lungfish can be extremely long-lived. A Queensland lungfish called "Granddad" at the Shedd Aquarium in Chicago was part of the permanent live collection from 1933 to 2017 after a previous residence at the Sydney Aquarium ; at 109 years old, it was euthanized following a decline in health consistent with old age. As of 2022,

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