Lungfish

Australian lungfish ( Neoceratodus forsteri )

The lungfish ( Dipnoi ) are a subclass of bony fish ( Osteichthyes ), which occurs with six extant species in Africa, South America and Australia. Their closest living relatives are the coelacanth ( Crossopterygiformes ) and the land vertebrates ( Tetrapoda ). The scientific name is the Latinized masculine plural form of the Greek word art δίπνοος, dípnoos back and means " Doppelatmer " because the lungfish gills for respiration in water and have lungs to breathe air from the water surface. The German name lungfish derives from the fact that they have a simply constructed lungs.

Discovery history

Fossil lungfish from the Old Red Sandstone have been known for more than 200 years. The South American lungfish became the first living species discovered in 1836 by the Austrian zoologist Johann Natterer and 1837, described by his colleagues Leopold Fitzinger, which struck the lungs as well as the unusual position of the external nasal openings near the upper lip as a reptile. The first scientists were given the living lungfish to face, could not believe that they had fish on. Fitzinger had no doubt that the South American lungfish is a reptile, especially as at that time the " critters " not yet clear difference in amphibians and reptiles. The scientific name means Lepidosiren shed Newt, and this name persisted long in German, for example, in Brehm's Animal Life.

The British zoologist Richard Owen, in 1839 the African lungfish described, then realized that the animals have to be fish. The Australian lungfish was finally found in 1870 in Queensland, 32 years after its close relative Triassic Ceratodus was described by Swiss paleontologist Louis Agassiz based his tooth plates. Albert Günther in 1871 published an accurate anatomical description of the Australian lung fish and fish confirmed the nature of the animals.

Physique

The recent lungfish are 44 centimeters to 1.70 meters long. In all six species, the dorsal fin, the caudal fin protocerke and the anal fin are merged to form one Flossensaum. In contrast, had the lungfish of Devon distinctly separate dorsal, anal and caudal fins, which were still heterocercal. The Australian lungfish, breast and pelvic fins that are supported by a partially ossified and provided with muscles skeleton. For the other five species, the paired fins are transformed into thread-like organs without fin rays.

The Australian lungfish has large diamond-shaped scales, the scales of the remaining species are small and are deeply embedded in a glandular epidermis.

The lungs of lungfish is an organ of the intestine, which is homologous to the swim bladder is. The Australian lungfish has a single lung, which is above the intestine. The remaining species have paired lungs, which lie towards the abdomen. In general, increase lung fish on every 30 to 60 minutes to the water surface to breathe air.

The African and South American lungfish have as a larva external gill filaments, but which are then regressed. Some species are dependent on air breathing. If they are held too long under water, they suffocate - one for fish rather unusual property. Their gills they use primarily for the delivery of carbon dioxide to the regulation of the acid -base balance and nitrogenous waste products for delivery.

The body of the lungfish is elongated, externally to males and females do not differ. A special feature of the Dipnoi is the lymphatic system, which they share with the tetrapods, but not with the other fish - have arisen at so it must be in Devon, after the separation of the bony fishes in Actino - (ray- finned fishes) and Sarcopterygii (meat -finned fishes).

Way of life

Lungfish are very lazy animals that inhabit mainly small standing or slowly flowing waters. Only the Ethiopian lungfish ( Protopterus aethiopicus ) also inhabits large lakes, such as Lake Tanganyika. Lung fish feed carnivorous and eat slow demersal fish, mussels, snails, worms, crustaceans and insect larvae.

It has been reported that African lungfish can encapsulate up to four years as a panel of the body's own mucus and mud cover. For this purpose, they dig into the mud and excrete mucus. This solidifies and the clothes dug into the mud corridor. In the vicinity of the mouth is a hole through which the pulmonary respiration becomes possible. During this period, they live by their muscle tissue and store their waste products, which they extract the water and perform their cycle. You balls together and hold her tail over his eyes struck to protect them from drying out. After a period such they look like dried fish and it takes several hours until they can move again.

Australian lungfish ( Neoceratodus ) can, in contrast to their relatives, the South American lungfish ( Lepidosiren ) and the African lungfish ( Protopterus ), not encapsulate because of drought in mud and survive there.

Reproduction

Lungfish multiply oviparous and lay up to 5000 eggs per nest. The eggs of the Australian and the African lung fish have a diameter of 3 to 4 mm, which are the South American lung fish greater than 6 to 7 mm. The eggs are wrapped in the Müllerian duct of a gelatinous substance. African and South American lungfish build horizontal transitions in the banks of the waters into which the eggs are laid. The Australian lungfish she sticks to water plants. Its larvae hatch after 25 to 30 days. They have no external gills, while the other two genera with three or four external gills have tufts.

Evolution

In the Palaeozoic era ( Paleozoic ) were distributed both in the sea and in freshwater lungfish. The first lungfish are known from the geological age of the Devonian from the Chinese Yunnan province. From this time, the first, however, empty capsules fossil mud come. In such preserved lungfish are only known from the Permian.

Most species died out at the great mass extinction in the transition to the Mesozoic era ( Mesozoic ). Only two groups survived, which have survived to this day. The Neoceratodontidae which are now represented only with a kind, in the Mesozoic had a worldwide distribution.

The relatively close relative of coelacanth and lungfish, the Rhipidistia be viewed in paleontology often as ancestors of the first land vertebrates ( Tetrapoda ). The structure of their skeleton is similar to Ichthyostega, a fossil which is considered to be one of the first amphibians and hence as a land vertebrate. Tiktaalik is a transitional form between coelacanths and land vertebrates.

For a close relationship of the lung fish with terrestrial vertebrates also speak a number of common features, in particular the skull structure, the approach of separation of oxygen-rich blood from the lungs and oxygen-poor blood from the body and the four approximately equal extremities and in the form position the legs of land vertebrates correspond.

1996 analysis was published, after the genetic material of the lung fish is close to the phylogenetic root of all vertebrates. The surviving species of lungfish have the most complex genome of all known living organisms because their genetic material is partly about twenty times larger than that of a human.

Genome size

The South American lungfish has 80 picograms ( 7.84 × 1010 base pairs), the largest known animal genome. Older, but probably less accurate studies show with about 133 picograms even larger genomes that have been found in African style Ethiopian lungfish.

System

The recent lungfish and their immediate ancestors are summarized in the superorder Ceratodontimorpha and order Ceratodontiformes. They occur in six species in Africa, Australia and South America. They are divided into three families and three genera, and there are four representatives of a genus in Africa:

• Order Ceratodontiformes Family Ceratodontidae Ceratodus ( Triassic)

• Australian lungfish ( Neoceratodus forsteri )

• Family Lepidosirenidae South American lungfish ( Lepidosiren paradoxa )

• Ethiopian lungfish ( Protopterus aethiopicus )
• East African lungfish ( Protopterus amphibius)
• West African lungfish ( Protopterus annectens )
• Congo lungfish ( Protopterus dolloi )

The phylogenetic relationships of the species alive today lineage can be found in the following diagram:

South American lungfish ( Lepidosiren paradoxa )

Ethiopian lungfish ( Protopterus aethiopicus )

East African lungfish ( Protopterus amphibius)

African lungfish ( Protopterus annectens )

Congo lungfish ( Protopterus dolloi )

Australian lungfish ( Neoceratodus forsteri )