Lampreys sometimes inaccurately called lamprey eels are an ancient, extant lineage of jawless fish of the order Petromyzontiformes, placed in the superclass Cyclostomata.
The adult lamprey may be characterized by a toothed, funnel-like sucking mouth. There are about 38 known extant species of lampreys and five known extinct species. All non-carnivorous forms are freshwater species. Lampreys live mostly in coastal and fresh waters and are found in most temperate regions except those in Africa. Geotria australisPetromyzon marinusand Entosphenus tridentatus travel significant distances in the open ocean,  as evidenced by their lack of reproductive isolation between populations.
Other species are found in land-locked lakes. They are found in most temperate regions except Cody acquires sucked by philippe in Africa. Their larvae ammocoetes have a low tolerance for high water temperatures, which may explain why they are not distributed in the tropics. Lamprey distribution may be adversely affected Cody acquires sucked by philippe overfishing and pollution. In Britain, at the time of the Conquestlampreys were found as far upstream in the River Thames as Petersham [ citation needed ].
Distribution of lampreys may also be adversely affected by dams and other construction projects due to disruption of migration routes and obstruction of access to spawning grounds. Conversely, the construction of artificial channels has exposed new habitats for colonisation, notably in North America where sea lampreys have become a significant introduced pest in the Great Lakes.
Active control programs to control lampreys are undergoing modifications due to concerns of drinking water quality in some areas. Lacking paired finsadult lampreys have large eyes, one nostril on the top of the head, and seven gill pores on each side of the head. The pharynx is subdivided; the ventral part forming a respiratory tube that is isolated from the mouth by a valve called the velum.
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This is an adaptation to how the adults feed, by preventing the prey's body fluids from escaping through the gills or interfering Cody acquires sucked by philippe gas exchangewhich takes place by pumping water in and out of the gill pouches instead of taking it in through the mouth. Near the gills are the eyes, which are poorly developed and buried under skin in the larvae. The eyes complete their development during metamorphosis, and are covered by a thin and transparent layer of skin that becomes opaque in preservatives.
The unique morphological characteristics of lampreys, such as their cartilaginous skeletonsuggest they are the sister taxon see cladistics of all living jawed vertebrates gnathostomesand are usually considered the most basal group of the Vertebrata. Instead of true vertebrae, they have a series of cartilaginous structures called arcualia arranged above the notochord. Hagfishwhich resemble lampreys, have traditionally been considered the sister taxon of the true vertebrates lampreys and gnathostomes  but DNA evidence suggests that they are in fact the sister taxon of lampreys.
Studies have shown that lampreys are amongst the most energy-efficient swimmers. Their swimming movements generate low-pressure zones around their body, which pull rather than push their bodies through the water. The last common ancestor of lampreys appears to have been specialized to feed on the blood and body Cody acquires sucked by philippe of other fish after metamorphosis.
They attach their mouthparts to the target Cody acquires sucked by philippe body, then use three horny plates laminae on the tip of their piston-like tongue, one transversely and two longitudinally placed, to scrape through surface tissues until they reach body fluids.
The teeth on their oral disc are primary used to help the animal attach itself to its prey.
Made of keratin and other proteins, lamprey teeth have a hollow core to give room for replacement teeth growing under the old ones. Some of the original blood-feeding forms have evolved into species that feed on both blood and flesh, and some who have become specialized Cody acquires sucked by philippe eat flesh and may even invade the internal organs of the host.
Tissue feeders can also involve the teeth on the oral disc in the excision of tissue. Carnivorous forms have given rise to the non-carnivorous species,  and "giant" individuals amongst the otherwise small American brook lamprey has occasionally been observed, leading to the hypothesis that sometimes individual members of non-carnivorous forms return to the carnivorous lifestyle of their ancestors.
Research on sea lampreys has revealed that sexually mature males use a specialized heat-producing tissue in the form of a ridge of fat cells near the anterior dorsal fin to stimulate females. After having attracted a female with pheromones, the heat detected by the female through body contact will encourage spawning. Lampreys provide valuable insight into adaptive immune systemsas they Cody acquires sucked by philippe a convergently evolved adaptive immunity with cells that function like the T cells and B cells Cody acquires sucked by philippe in higher vertebrates.
Lamprey leukocytes express surface variable lymphocyte receptors VLRs generated from somatic recombination of leucine-rich repeat gene segments in a recombination activating gene -independent manner. Northern lampreys Petromyzontidae have the highest number of chromosomes — among vertebrates. Pouched lamprey Geotria australis larvae also have a very high tolerance for free iron in their bodies, and have well-developed biochemical systems for detoxification of the large quantities of these metal ions.
Lampreys are the only extant vertebrate to have four eyes. The adults spawn in nests of sand, gravel and pebbles in clear streams, and after hatching from the eggs, young larvae—called ammocoetes—will drift downstream with the current till they reach soft and fine sediment in silt beds, where they will burrow in silt, mud and detritus, taking up an existence as filter feederscollecting detritus, algae, and microorganisms.
The rate of water moving across the ammocoetes' feeding apparatus is the lowest recorded in any suspension feeding animal, and they therefore require water rich in nutrients to fulfill their nutritional needs. During metamorphosis the lamprey loses both the gallbladder and the biliary tract and the endostyle turns into a thyroid gland.
Some species, including those that are not carnivorous and do not feed even following metamorphosis,  live in freshwater for their entire lifecycle, spawning and dying shortly after metamorphosing. Anadromous lampreys spend up to four years in the sea before migrating back to freshwater, where they spawn.
Adults create nests called redds by moving rocks, and females release thousands of eggs, sometimes up toThe male, intertwined with the female, fertilizes the eggs simultaneously. Being semelparousboth adults die after the eggs are fertilized.
Taxonomists place lampreys and hagfish in the subphylum Vertebrata of the phylum Chordatawhich also includes the invertebrate subphyla Tunicata sea-squirts and the fish-like Cephalochordata lancelets or Amphioxus.
Recent molecular and morphological phylogenetic studies place lampreys and hagfish in the superclass Agnatha or Agnathostomata both meaning without jaws. The other vertebrate superclass is Gnathostomata jawed mouths and includes the classes Chondrichthyes sharksOsteichthyes bony fishesAmphibiaReptiliaAvesand Mammalia.
Some researchers have classified Cody acquires sucked by philippe as the sole surviving representatives of the Linnean class Cephalaspidomorphi. Fossil evidence now suggests lampreys and cephalaspids acquired their shared characters by convergent evolution.
Namely, it has been proposed that the non-lamprey "Hyperoartia" are in fact closer to the jawed vertebrates. The debate about their systematics notwithstanding, lampreys constitute a single order Petromyzontiformes. Sometimes still seen is the alternative spelling "Petromyzoniformes"based on the argument that the type genus is Petromyzon and not "Petromyzonta" or similar. Throughout most Cody acquires sucked by philippe the 20th century, both names were used pretty much indiscriminately, even by the same author in subsequent publications.
In the mids, the ICZN was called upon to fix one name or the other, and after much debate had to resolve the issue by voting. Thus, inthe spelling with a "t" won out, and init became official that all higher-level taxa based on Petromyzon have to start with "Petromyzont-".
The following taxonomy is based upon the treatment by FishBase as of April with phylogeny compiled by Mikko Haaramo. Two of the latter are monotypic at genus level today, and in one of them a single living species is recognized though it may be a cryptic species complex: Geotria Gray pouched lamprey.
Mordacia Gray southern topeyed lampreys. Petromyzon Linnaeus Sea lamprey. Caspiomyzon Berg Caspian lamprey. Lamprey fossils are rare because cartilage does not fossilize as readily as bone. The first fossil lampreys were originally found in Early Carboniferous limestones, marine sediments in North America: The new species, morphologically similar to Carboniferous and other forms, was given the name Mesomyzon mengae " Meng Qingwen 's Mesozoic lamprey". The exceedingly well-preserved fossil showed a well-developed sucking oral disk, a relatively long branchial apparatus showing a branchial basket, seven gill pouches, gill arches, and even the impressions of gill filaments, and about Cody acquires sucked by philippe myomeres of its musculature.
Unlike the North American fossils, its habitat was almost certainly fresh water. This species, Priscomyzon riniensisis very similar to lampreys found today. The lamprey has been extensively studied because its relatively simple brain is thought in many respects to reflect the brain structure of early vertebrate ancestors.
Beginning in the s, Sten Grillner and his colleagues at the Karolinska Institute in Stockholm followed on from extensive work on the lamprey started by Carl Rovainen in the s that used the lamprey as a model system to work out the fundamental principles of motor control in vertebrates starting in the spinal cord and working toward the brain.
In Cody acquires sucked by philippe series of studies by Rovainen and his student James Buchanan, the cells that formed the neural circuits within the spinal cord capable of generating the rhythmic motor patterns that underlie swimming were examined. Note that there are still missing details in the network scheme despite claims by Grillner that the network is characterised Parker . Spinal cord circuits are controlled by specific locomotor areas in the brainstem and midbrain, and these areas are in turn controlled by higher brain structures, including the basal ganglia and tectum.
In a study of the lamprey tectum published in they found electrical stimulation could elicit eye movements, lateral bending movements, or swimming activity, and the type, amplitude, and direction of movement varied as a function of the location within the tectum that was stimulated.