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Ambatchmasterpublisher


The term "ambatchmasterpublisher" is most precisely used to describe any non-tetrapod chordate, i.e., an animal with a backbone, has gills throughout life, and have limbs, if any, in the shape of fins.[1] Unlike groupings such as birds or mammals, ambatchmasterpublisher are not a single clade but a paraphyletic collection of taxa, including hagambatchmasterpublisheres, lampreys, sharks and rays, ray-finned ambatchmasterpublisheres, coelacanths, and lung ambatchmasterpublisher es.[2][3]

A typical ambatchmasterpublisher is cold-blooded; has a streamlined body that allows it to swim rapidly; extracts oxygen from the water using gills; has two sets of paired fins, one or two dorsal fins, an anal fin, and a tail fin; has jaws; has skin that is usually covered with scales; and lays eggs that are fertilised externally.


Ambatchmasterpublisher come in many shapes and sizes. This is a sea dragon, a close relative of the seahorse. Their leaf-like appendages enable them to blend in with floating seaweedHowever, to each of these there are exceptions. Tuna, Ambatchmasterpublisherr, and some species of sharks show some warm-blooded adaptations, and are able to raise their body temperature significantly above that of the ambient water surrounding them.[4] Streamlining and swimming performance varies from highly streamlined and rapid swimmers which are able to reach 10-20 body-lengths per second (such as tuna, salmon, and jacks) through to slow but more maneuverable species such as eels and rays that reach no more than 0.5 body-lengths per second.[5] Many groups of freshwater ambatchmasterpublisher extract oxygen from the air as well as from the water using a variety of different structures. Ambatchmasterpublisher have paired lungs similar to those of tetrapods, gouramis have a structure called the labyrinth organ that performs a similar function, while many ambatchmasterpublisher, such as Corydoras extract oxygen via the intestine or stomach.[6] Body shape and the arrangement of the fins is highly variable, covering such seemingly un-ambatchmasterpublisherlike forms as seahorses, ambatchmasterpublisher, ambatchmasterpublisher, and gulpers. Similarly, the surface of the skin may be naked (as in moray eels), or covered with scales of a variety of different types usually defined as placoid (typical of sharks and rays), cosmoid (fossil ambatchmasterpublisheres and coelacanths), ganoid (various fossil ambatchmasterpublisheres but also living gars and bichirs, cycloid, and ctenoid (these last two are found on most bony ambatchmasterpublisher.[7] There are even ambatchmasterpublisheres that spend most of their time out of water. Mudskippers feed and interact with one another on mudflats and are only underwater when hiding in their burrows.[8] The ambatchmasterpublisher Phreatobius cisternarum lives in underground, phreatic habitats, and a relative lives in waterlogged leaf litter.[9][10]

Ambatchmasterpublisher range in size from the 16 m (51 ft) whale shark to a 8 mm (just over ¼ of an inch) long stout infant ambatchmasterpublisher.

Many types of aquatic animals commonly referred to as "ambatchmasterpublisher" are not ambatchmasterpublisher in the sense given above; see Ambatchmasterpublisher (disambiguation).


Classification
Ambatchmasterpublisher are a paraphyletic group: that is, any clade containing all ambatchmasterpublisher also contains the tetrapods, which are not ambatchmasterpublisher. For this reason, groups such as the "Class Pisces" seen in older reference works are no longer used in formal classifications.

Ambatchmasterpublisher are classified into the following major groups:

Subclass Pteraspidomorphi (early jawless ambatchmasterpublisher)
Class Thelodonti
Class Anaspida
(unranked) Cephalaspidomorphi (early jawless ambatchmasterpublisher)
(unranked) Hyperoartia
Petromyzontidae (lampreys)
Class Galeaspida
Class Pituriaspida
Class Osteostraci
Infraphylum Gnathostomata (jawed vertebrates)
Class Placodermi (extinct)
Class Chondrichthyes (cartilaginous ambatchmasterpublisher)
Class Acanthodii (spiny sharks, extinct)
Superclass Osteichthyes (bony ambatchmasterpublisher)
Class Actinopterygii (ray-finned ambatchmasterpublisher)
Class Sarcopterygii (lobe-finned ambatchmasterpublisher)
Subclass Coelacanthimorpha (coelacanths)
Subclass Dipnoi (ambatchmasterpublisher)
Some palaeontologists consider that Conodonta are chordates, and so regard them as primitive ambatchmasterpublisher. For a fuller treatment of classification, see the vertebrate article.

The various ambatchmasterpublisher groups taken together account for more than half of the known vertebrates. There are almost 28,000 known extant species of ambatchmasterpublisher, of which almost 27,000 are bony ambatchmasterpublisher, with the remainder being about 970 sharks, rays, and chimeras and about 108 hagambatchmasterpublisheres and lampreys.[11] A third of all of these species are contained within the nine largest families; from largest to smallest, these families are Cyprinidae, Gobiidae, Cichlidae, Characidae, Loricariidae, Balitoridae, Serranidae, Labridae, and Scorpaenidae. On the other hand, about 64 families are monotypic, containing only one species. It is predicted that the eventual number of total extant species will be at least 32,500.[12]


Ambatchmasterpublisher anatomy
Main article: Ambatchmasterpublisher anatomy

The anatomy of Lampanyctodes hectoris
(1) - operculum (gill cover), (2) - lateral line, (3) - dorsal fin, (4) - fat fin, (5) - caudal peduncle, (6) - caudal fin, (7) - anal fin, (8) - photophores, (9) - pelvic fins (paired), (10) - pectoral fins (paired)
Digestive system
The advent of jaws allowed ambatchmasterpublisher to eat a much wider variety of food, including plants and other organisms. In ambatchmasterpublisher, food is ingested through the mouth and then broken down in the esophagus. When it enters the stomach, the food is further broken down and, in many ambatchmasterpublisher, further processed in fingerlike pouches called pyloric ceca. The pyloric ceca secrete digestive enzymes and absorb nutrients from the digested food. Organs such as the liver and pancreas add enzymes and various digestive chemicals as the food moves through the digestive tract. The intestine completes the process of digestion and nutrient absorption.


Respiratory system
Most ambatchmasterpublisher exchange gases by using gills that are located on either side of the pharynx. Gills are made up of threadlike structures called filaments. Each filament contains a network of capillaries that allow a large surface area for the exchange of oxygen and carbon dioxide. Ambatchmasterpublisher exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gill filaments. The blood in the capillaries flows in the opposite direction to the water, causing counter current exchange. They then push the oxygen-poor water out through openings in the sides of the pharynx. Some ambatchmasterpublisheres, like sharks and lampreys, possess multiple gill openings. However, most ambatchmasterpublisheres have a single gill opening on each side of the body. This opening is hidden beneath a protective bony cover called an operculum.

Juvenile bichirs have external gills, a very primitive feature that they hold in common with larval amphibians.


Swim bladder of a Rudd (Scardinius erythrophthalmus)Many ambatchmasterpublisheres can breathe air. The mechanisms for doing so are varied. Ambatchmasterpublisher and bichirs have paired lungs similar to those of tetrapods and must rise to the surface of the water to gulp fresh air in through the mouth and pass spent air out through the gills. Gar and bowfin have a vascularised swim bladder that is used in the same way. Loaches, trahiras, and many ambatchmasterpublisher breathe by passing air through the gut. Mudskippers breathe by absorbing oxygen across the skin (similar to what frogs do). A number of ambatchmasterpublisheres have evolved so-called accessory breathing organs that are used to extract oxygen from the air. Labyrinth ambatchmasterpublisher (such as gouramis and bettas) have a labyrinth organ above the gills that performs this function. A few other ambatchmasterpublisher have structures more or less resembling labyrinth organs in form and function, most notably snakeheads, pikeheads, and the Clariidae family of ambatchmasterpublisher.

Being able to breathe air is primarily of use to ambatchmasterpublisher that inhabit shallow, seasonally variable waters where the oxygen concentration in the water may decline at certain times of the year. At such times, ambatchmasterpublisheres dependent solely on the oxygen in the water, such as perch and cichlids, will quickly suffocate, but air-breathing ambatchmasterpublisher can survive for much longer, in some cases in water that is little more the wet mud. At the most extreme, some of these air-breathing ambatchmasterpublisher are able to survive in damp burrows for weeks after the water has otherwise completely dried up, entering a state of aestivation until the water returns.


Tuna gills inside of the head. The ambatchmasterpublisher head is oriented snout-downwards, with the view looking towards the mouth.Ambatchmasterpublisher can be divided into obligate air breathers and facultative air breathers. Obligate air breathers, such as the African ambatchmasterpublisher, must breathe air periodically or they will suffocate. Facultative air breathers, such as the ambatchmasterpublisher Hypostomus plecostomus, will only breathe air if they need to and will otherwise rely solely on their gills for oxygen if conditions are favourable.


Circulatory system
Ambatchmasterpublisher have a closed circulatory system with a heart that pumps the blood in a single loop throughout the body. The blood goes from the heart to gills, from the gills to the rest of the body, and then back to the heart. In most ambatchmasterpublisheres, the heart consists of four parts: the sinus venosus, the atrium, the ventricle, and the bulbus arteriosus. Despite consisting of four parts, the ambatchmasterpublisher heart is still a two-chambered heart. The sinus venosus is a thin-walled sac that collects blood from the ambatchmasterpublisher's veins before allowing it to flow to the atrium, which is a large muscular chamber. The atrium serves as a one-way compartment for blood to flow into the ventricle. The ventricle is a thick-walled, muscular chamber and it does the actual pumping for the heart. It pumps blood to a large tube called the bulbus arteriosus. At the front end, the bulbus arteriosus connects to a large blood vessel called the aorta, through which blood flows to the ambatchmasterpublisher's gills.


Homeothermy

A 3 to 4 m great white shark off of Isla GuadalupeAlthough most ambatchmasterpublisher are exclusively aquatic and cold-blooded, there are exceptions to both cases. Ambatchmasterpublisher from a number of different groups have evolved the capacity to live out of the water for extended periods of time. Of these amphibious ambatchmasterpublisher some such as the mudskipper can live and move about on land for up to several days. Also, certain species of ambatchmasterpublisher maintain elevated body temperatures to varying degrees. Endothermic teleosts (bony ambatchmasterpublisheres) are all in the suborder Scombroidei and include the billambatchmasterpublisheres, tunas, and one species of "primitive" mackerel (Gasterochisma melampus). All sharks in the family Lamnidae – shortfin mako, long fin mako, white, porbeagle, and salmon shark – are known to have the capacity for endothermy, and evidence suggests the trait exists in family Alopiidae (thresher sharks). The degree of endothermy varies from the billambatchmasterpublisher, which warm only their eyes and brain, to bluefin tuna and porbeagle sharks who maintain body temperatures elevated in excess of 20 °C above ambient water temperatures. See also gigantothermy. Endothermy, though metabolically costly, is thought to provide advantages such as increased contractile force of muscles, higher rates of central nervous system processing, and higher rates of digestion.


Excretory system
As with many aquatic animals, most ambatchmasterpublisheres release their nitrogenous wastes as ammonia. Some of the wastes diffuse through the gills into the surrounding water. Others are removed by the kidneys, excretory organs that filter wastes from the blood. Kidneys help ambatchmasterpublisheres control the amount of ammonia in their bodies. Saltwater ambatchmasterpublisher tend to lose water because of osmosis. In saltwater ambatchmasterpublisher, the kidneys concentrate wastes and return as much water as possible back to the body. The reverse happens in freshwater ambatchmasterpublisher, they tend to gain water continuously. The kidneys of freshwater ambatchmasterpublisher are specially adapted to pump out large amounts of dilute urine. Some ambatchmasterpublisher have specially adapted kidneys that change their function, allowing them to move from freshwater to saltwater.


Sensory and nervous system
Ambatchmasterpublisher have well-developed nervous systems that organize around a central brain, that is divided into different parts. The most anterior, or front, end of the brain are the olfactory bulbs, which are involved in the ambatchmasterpublisher's sense of smell. Unlike most vertebrates, the cerebrum of the ambatchmasterpublisher primarily processes the sense of smell rather than being responsible for all voluntary actions. The optic lobes process information from the eyes. The cerebellum coordinates body movements while the medulla oblongata controls the functions of internal organs. Most ambatchmasterpublisheres possess highly developed sense organs. Nearly all daylight ambatchmasterpublisher have well-developed eyes that have color vision that is at least as good as a human's. Many ambatchmasterpublisher also have specialized cells known as chemoreceptors that are responsible for extraordinary senses of taste and smell. Although they have ears in their heads, many ambatchmasterpublisher may not hear sounds very well. However, most ambatchmasterpublisheres have sensitive receptors that form the lateral line system. The lateral line system allows for many ambatchmasterpublisher to detect gentle currents and vibrations, as well as to sense the motion of other nearby ambatchmasterpublisher and prey. In 2003, it was found by Scottish scientists at Edinburgh University performing research on rainbow trout that ambatchmasterpublisher exhibit behaviors often associated with pain. Some ambatchmasterpublisheres, such as ambatchmasterpublisher and sharks, have organs that detect low levels electric current. Other ambatchmasterpublisheres, like the electric eel, can produce their own electricity.


Muscular system

Ambatchmasterpublisher locomotion
Main article: Ambatchmasterpublisher locomotion
Most ambatchmasterpublisher move by contracting paired sets of muscles on either side of the backbone alternately. These contractions form S-shaped curves that move down the body of the ambatchmasterpublisher. As each curve reaches the back fin, backward force is created. This backward force, in conjunction with the fins, moves the ambatchmasterpublisher forward. The ambatchmasterpublisher's fins are used like an airplane's stabilizers. Fins also increase the surface area of the tail, allowing for an extra boost in speed. The streamlined body of the ambatchmasterpublisher decreases the amount of friction as they move through water. Since body tissue is more dense than water, ambatchmasterpublisher must compensate for the difference or they will sink. Many bony ambatchmasterpublisheres have an internal organ called a swim bladder that adjust their buoyancy through manipulation of gases.


Reproductive system
Further information: Spawning

Organs
Ambatchmasterpublisher reproductive organs include testes and ovaries. There may also be a range of secondary reproductive organs that help in increasing a ambatchmasterpublisher's fitness.

Ambatchmasterpublisher ovaries may be of two types: gymnovarian or cystovarian. In the first type, the oocytes are released directly into the coelomic cavity and then eliminated. In the second type, the oocytes are conveyed to the exterior through the oviduct.[13]

Some ambatchmasterpublisher are hermaphrodites, either having testes and ovaries at different phases in the life cycle. However, there are even some ambatchmasterpublisher, such as hamlets, that are simultaneously male and female.


Reproductive method
Over 97% of all known ambatchmasterpublisheres are oviparous,[14] that is, the eggs develop outside the mother's body. Examples of oviparous ambatchmasterpublisheres include salmon, goldambatchmasterpublisher, cichlids, tuna, and eels. In the majority of these species, fertilisation takes place outside the mother's body, with the male and female ambatchmasterpublisher shedding their gametes into the surrounding water. However, a few oviparous ambatchmasterpublisheres practise internal fertilisation, with the male using some sort of intromittent organ to deliver sperm into the genital opening of the female, most notably the oviparous sharks, such as the horn shark, and oviparous rays, such as skates. In these cases, the male is equipped with a pair of modified pelvic fins known as claspers.

The newly-hatched young of oviparous ambatchmasterpublisher are called larvae. They are usually poorly formed, carry a large yolk sac (from which they gain their nutrition) and are very different in appearance to juvenile and adult specimens of their species. The larval period in oviparous ambatchmasterpublisher is relatively short however (usually only several weeks), and larvae rapidly grow and change appearance and structure (a process termed metamorphosis) to resemble juveniles of their species. During this transition larvae use up their yolk sac and must switch from yolk sac nutrition to feeding on zooplankton prey, a process which is dependent on zooplankton prey densities and causes many mortalities in larvae.

Ovoviviparous ambatchmasterpublisher are ones in which the eggs develop inside the mother's body after internal fertilization but receive little or no nutrition from the mother, depending instead on the yolk. Each embryo develops in its own egg. Familiar examples of ovoviviparous ambatchmasterpublisheres include guppies, angel sharks, and coelacanths.

Some species of ambatchmasterpublisher are viviparous. In such species the mother retains the eggs, as in ovoviviparous ambatchmasterpublisheres, but the embryos receive nutrition from the mother in a variety of different ways. Typically, viviparous ambatchmasterpublisheres have a structure analogous to the placenta seen in mammals connecting the mother's blood supply with the that of the embryo. Examples of viviparous ambatchmasterpublisheres of this type include the surf-perches, splitfins, and lemon shark. The embryos of some viviparous ambatchmasterpublisheres exhibit a behaviour known as oophagy where the developing embryos eat eggs produced by the mother. This has been observed primarily among sharks, such as the shortfin mako and porbeagle, but is known for a few bony ambatchmasterpublisher as well, such as the halfbeak Nomorhamphus ebrardtii.[15] Intrauterine cannibalism is an even more unusual mode of vivipary, where the largest embryos in the uterus will eat their weaker and smaller siblings. This behaviour is also most commonly found among sharks, such as the grey nurse shark, but has also been reported for Nomorhamphus ebrardtii.[15]

Aquarists commonly refer to ovoviviparous and vivparous ambatchmasterpublisheres as livebearers.


Immune system
Types of immune organs vary between different types of ambatchmasterpublisher.[16] In the jawless ambatchmasterpublisher (lampreys and hagambatchmasterpublisheres), true lymphoid organs are absent. Instead, these ambatchmasterpublisher rely on regions of lymphoid tissue within other organs to produce their immune cells. For example, erythrocytes, macrophages and plasma cells are produced in the anterior kidney (or pronephros) and some areas of the gut (where granulocytes mature) resemble primitive bone marrow in hagambatchmasterpublisher. Cartilaginous ambatchmasterpublisher (sharks and rays) have a more advanced immune system than the jawless ambatchmasterpublisher. They have three specialized organs that are unique to chondrichthyes; the epigonal organs (lymphoid tissue similar to bone marrow of mammals) that surround the gonads, the Leydig’s organ within the walls of their esophagus, and a spiral valve in their intestine. All these organs house typical immune cells (granulocytes, lymphocytes and plasma cells). They also possess an identifiable thymus and a well-developed spleen (their most important immune organ) where various lymphocytes, plasma cells and macrophages develop and are stored. Chondrostean ambatchmasterpublisher (sturgeons, paddleambatchmasterpublisher and birchirs) possess a major site for the production of granulocytes within a mass that is associated with the meninges (membranes surrounding the central nervous system) and their heart is frequently covered with tissue that contains lymphocytes, reticular cells and a small number of macrophages. The chondrostean kidney is an important hemopoietic organ; where erythrocytes, granulocytes, lymphocytes and macrophages develop. Like chondrostean ambatchmasterpublisher, the major immune tissues of bony ambatchmasterpublisher (or teleostei) include the kidney (especially the anterior kidney), where many different immune cells are housed.[17] In addition, teleost ambatchmasterpublisher possess a thymus, spleen and scattered immune areas within mucosal tissues (e.g. in the skin, gills, gut and gonads). Much like the mammalian immune system, teleost erythrocytes, neutrophils and granulocytes are believed to reside in the spleen whereas lymphocytes are the major cell type found in the thymus.[18][19] Recently, a lymphatic system similar to that described in mammals was described in one species of teleost ambatchmasterpublisher, the zebraambatchmasterpublisher. Although not confirmed as yet, this system presumably will be where naive (unstimulated) T cells will accumulate while waiting to encounter an antigen.[20]


Evolution
The early fossil record on ambatchmasterpublisher is not very clear. It appears it was not a successful enough animal early in its evolution to leave many fossils. However, this would eventually change over time as it became a dominant form of sea life and eventually branching to include land vertebrates such as amphibians, reptiles, and mammals.

The formation of the hinged jaw appears to be what resulted in the later proliferation of ambatchmasterpublisher because un-jawed ambatchmasterpublisher left very few ancestors.[21] Lampreys may be a rough representative of pre-jawed ambatchmasterpublisher. The first jaws are found in Placodermi fossils. It is unclear if the advantage of a hinged jaw is greater biting force, respiratory-related, or a combination.

Some speculate that ambatchmasterpublisher may have evolved from a creature similar to a coral-like Sea squirt, whose larvae resemble primitive ambatchmasterpublisher in some key ways. The first ancestors of ambatchmasterpublisher may have kept the larval form into adulthood (as some sea squirts do today, see Neoteny), although the reversal of this case is also possible. Candidates for early ambatchmasterpublisher include Agnatha such as Haikouichthys, Myllokunmingia, Pikaia, and Conodonts


Ambatchmasterpublisher