83-473: Lampreys / ˈ l æ m p r eɪ z / (sometimes inaccurately called lamprey eels ) are a group of jawless fish comprising the order Petromyzontiformes / ˌ p ɛ t r oʊ m ɪ ˈ z ɒ n t ɪ f ɔːr m iː z / . The adult lamprey is characterized by a toothed, funnel-like sucking mouth. The common name "lamprey" is probably derived from Latin lampetra , which may mean "stone licker" ( lambere "to lick" + petra "stone"), though
166-552: A diurnal cycle , becoming dark at day and pale at night. The skin also has photoreceptors , light sensitive cells, most of them concentrated in the tail, which helps them to stay buried. Lampreys may spend up to eight years as ammocoetes, while species such as the Arctic lamprey may only spend one to two years as larvae, prior to undergoing a metamorphosis which generally lasts 3–4 months, but can vary between species. While metamorphosing, they do not eat. The rate of water moving across
249-401: A notochord , dorsal hollow nerve cord , pharyngeal slits , pituitary gland / endostyle , and a post anal tail during the process of their development are considered to be chordates . Lampreys contain these characteristics that define them as chordates. Lamprey anatomy is very different based on what stage of development they are in. The notochord is derived from the mesoderm and is one of
332-681: A cheap dish in the United Kingdom . During the 1990s, their numbers collapsed across Europe. They became a delicacy, and the UK's most expensive species. Eels, particularly the moray eel , are popular among marine aquarists . Eel blood is toxic to humans and other mammals, but both cooking and the digestive process destroy the toxic protein. High consumption of eels is seen in European countries leading to those eel species being considered endangered. In 2010, Greenpeace International added
415-498: A dark-colored back, which enables them to blend in with the ground below when seen from above by a predator. Their light-colored undersides allow them to blend in with the bright air and water above them if a predator sees them from below. Lamprey coloration can also vary according to the region and specific environment in which the species is found. Some species can be distinguished by their unique markings – for example, Geotria australis individuals display two bluish stripes running
498-446: A dorsal or a caudal fin . Some fossil agnathans, such as osteostracans and pituriaspids , did have paired fins, a trait inherited in their jawed descendants . Fertilization in lampreys is external. Mode of fertilization in hagfishes is not known. Development in both groups probably is external. There is no known parental care. Not much is known about the hagfish reproductive process. It is believed that hagfish only have 30 eggs over
581-779: A junior synonym of vertebrata. The new phylogeny from Miyashita et al . (2019) is considered compatible with both morphological and molecular evidence. † Myllokunmingiidae [REDACTED] † Euphanerida [REDACTED] † Jamoytiiformes [REDACTED] † Endeiolepis † Birkeniiformes [REDACTED] † Paraconodontida † Proconodontida † Protopanderodontida † Panderontida † Paracordylodus † Balognathidae [REDACTED] † Prioniodinida † Ozarkodinida Hagfish [REDACTED] Lampreys [REDACTED] † Anatolepis † Arandaspida [REDACTED] † Astraspidiformes [REDACTED] † Tesakoviaspidida † Eriptychiida † Tesseraspidiformes Eel see text Eels are ray-finned fish belonging to
664-493: A lifetime. There is very little of the larval stage that characterizes the lamprey. Lamprey are only able to reproduce once. After external fertilization, the lamprey's cloacas remain open, allowing a fungus to enter their intestines, killing them . Lampreys reproduce in freshwater riverbeds, working in pairs to build a nest and burying their eggs about an inch beneath the sediment. The resulting hatchlings go through four years of larval development before becoming adults. Although
747-431: A long gut, more or less homogeneous throughout its length. Lampreys feed on other fish and mammals. Anticoagulant fluids preventing blood clotting are injected into the host, causing the host to yield more blood. Hagfish are scavengers, eating mostly dead animals. They use a row of sharp teeth to break down the animal. Because Agnathan teeth are unable to move up and down it limits their possible food types. In addition to
830-409: A minor element of modern marine fauna , agnathans were prominent among the early fish in the early Paleozoic . Two types of Early Cambrian animal apparently having fins, vertebrate musculature, and gills are known from the early Cambrian Maotianshan shales of China : Haikouichthys and Myllokunmingia . They have been tentatively assigned to Agnatha by Janvier. A third possible agnathid from
913-410: 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 a 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
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#1732780616167996-438: A single pair of regular eyes as well as two parietal eyes : a pineal and parapineal one (the exception is members of Mordacia ). The eyes of juvenile lampreys are poorly developed eyespot-like structures that are covered in non-transparent skin, while the eyes of adult lampreys are well developed. Accommodation is done by flattening the cornea, which pushes the lens towards the retina. The eye of family Mordaciidae possess just
1079-422: A single type of photoreceptor (rod-like), the family Petromyzontidae possess two photoreceptor types (a cone-like and a rod-like), and the family Geotriidae possesses five types of photoreceptors. The buccal cavity , anterior to the gonads , is responsible for attaching the animal, through suction, to either a stone or its prey. This then allows the tongue to make contact with the stone to rasp algae , or tear at
1162-444: A small number of radially arranged teeth, they lacked the specialised, heavily toothed discs with plate-like laminae present in modern lampreys, and it is possible that they fed by scraping algae off of animals, rather than feeding by predation/parasitism. They also lacked the modern three stage life cycle including ammocoetes found in modern lampreys, with the juvenile stages of these species closely resembling adults. Myxineidus from
1245-443: A sucking mouth. Those that are anadromous are carnivorous, feeding on fishes or marine mammals. 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 to 100,000. The male, intertwined with the female, fertilizes the eggs simultaneously. Being semelparous , both adults die after
1328-639: A thymus-like lympho-epithelial structure, termed thymoids. VLRB+ cells are B-cell-like, develop in hematopoietic organs, and differentiate into "VLRB antibody"-secreting plasma cells. Conodont (extinct) The taxon contains the subgroups Heterostraci , Astraspida , Arandaspida . Phylogeny based on the work of Mikko Haaramo and Delsuc et al. Hyperotreti / Myxini (hagfishes) Petromyzontomorpha (lampreys) ?† Conodonta † Pteraspidomorpha ?† Jamoytiiformes ?† Euphanerida † Anaspida † Thelodonti † Galeaspida † Pituriaspida † Osteostraci Gnathostomata (vertebrates with jaws) While
1411-567: Is a monophyletic group that originated among the deep-sea eels. The earliest fossil eels are known from the Late Cretaceous ( Cenomanian ) of Lebanon . These early eels retain primitive traits such as pelvic fins and thus do not appear to be closely related to any extant taxa. Body fossils of modern eels do not appear until the Eocene , although otoliths assignable to extant eel families and even some genera have been recovered from
1494-469: Is a paraphyletic infraphylum of non- gnathostome vertebrates , or jawless fish , in the phylum Chordata , subphylum Vertebrata , consisting of both living ( cyclostomes ) and extinct ( conodonts , anaspids , and ostracoderms , among others). Among recent animals , cyclostomes are sister to all vertebrates with jaws , known as gnathostomes . Molecular data , both from rRNA and from mtDNA as well as embryological data, strongly supports
1577-713: Is a traditional Māori food in New Zealand . In Italian cuisine , eels from the Valli di Comacchio , a swampy zone along the Adriatic coast, are especially prized, along with freshwater eels of Bolsena Lake and pond eels from Cabras, Sardinia . In northern Germany , the Netherlands , the Czech Republic , Poland , Denmark , and Sweden , smoked eel is considered a delicacy . Elvers, often fried, were once
1660-599: Is an adjective form of an older word, ελλυ, meaning "snake", which is directly comparable to Hittite ellu-essar- "snake pit". This myth likely came to Greece via Anatolia. In the Hittite version of the myth, the dragon is called Illuyanka : the illuy- part is cognate to the word illa , and the -anka part is cognate to angu , a word for "snake". Since the words for "snake" (and similarly shaped animals) are often subject to taboo in many Indo-European (and non-Indo-European) languages, no unambiguous Proto-Indo-European form of
1743-414: Is anterior to the intestines. It contains the sinus , one atrium , and one ventricle protected by the pericardial cartilages. The pineal gland , a photosensitive organ regulating melatonin production by capturing light signals through the photoreceptor cell converting them into intercellular signals of the lamprey is located in the midline of its body, for lamprey, the pineal eye is accompanied by
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#17327806161671826-735: Is no parental care in the Agnatha class. The Agnatha are ectothermic or cold, with a cartilaginous skeleton , and the heart contains 2 chambers. In modern agnathans, the body is covered in skin, with neither dermal or epidermal scales . The skin of hagfish has copious slime glands, the slime constituting their defense mechanism. The slime can sometimes clog up enemy fishes' gills, causing them to die. In direct contrast, many extinct agnathans sported extensive exoskeletons composed of either massive, heavy dermal armour or small mineralized scales. Almost all agnathans, including all extant agnathans , have no paired appendages, although most do have
1909-542: Is used as a metaphor for Nazi atrocities, and the sight of eels being killed by a fisherman triggers the madness of the protagonist's mother. Sinister implications of eels fishing are also referenced in Jo Nesbø 's Cockroaches , the second book of the Harry Hole detective series. The book's background includes a Norwegian village where eels in the nearby sea are rumored to feed on the corpses of drowned humans, making
1992-666: The Campanian and Maastrichtian , indicating some level of diversification among the extant groups prior to the Cretaceous-Paleogene extinction , which is also supported by phylogenetic divergence estimates. One of these otolith taxa, the mud-dwelling Pythonichthys arkansasensis , appears to have thrived in the aftermath of the K-Pg extinction, based on its abundance. Taxonomy based on Eschmeyer's Catalog of Fishes : Order Anguilliformes In some classifications,
2075-481: The European eel , Japanese eel , and American eel to its seafood red list. Japan consumes more than 70% of the global eel catch. The English name "eel" descends from Old English ǣl , Common Germanic *ēlaz . Also from the common Germanic are West Frisian iel , Dutch aal , German Aal , and Icelandic áll . Katz (1998) identifies a number of Indo-European cognates, among them
2158-639: The Middle Jurassic and the end of the Cretaceous . Modern lampreys spend the majority of their life in the juvenile "ammocoete" stage, where they burrow into the sediment and filter feed . Adult carnivorous lampreys are the most well-known species, and feed by boring into the flesh of other fish (or in rare cases marine mammals) to consume flesh and/or blood ; but only 18 species of lampreys engage in this predatory lifestyle (with Caspiomyzon suggested to feed on carrion rather than live prey). Of
2241-788: The Northeast . Freshwater eels, known as Kusia in Assamese , are eaten with curry, often with herbs. The European eel and other freshwater eels are mostly eaten in Europe and the United States , and is considered critically endangered. A traditional east London food is jellied eels , although the demand has significantly declined since World War II. The Spanish cuisine delicacy angulas consists of elver (young eels) sautéed in olive oil with garlic ; elvers usually reach prices of up to 1000 euro per kg. New Zealand longfin eel
2324-452: The T cells and B cells present in higher vertebrates immune system. 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. The adults spawn in nests of sand, gravel and pebbles in clear streams. After hatching from the eggs, young larvae—called ammocoetes—will drift downstream with
2407-487: The caudal fin, forming a single ribbon running along much of the length of the animal. Eels swim by generating waves that travel the length of their bodies. They can swim backward by reversing the direction of the wave. Most eels live in the shallow waters of the ocean and burrow into sand, mud, or amongst rocks. Most eel species are nocturnal , and thus are rarely seen. Sometimes, they are seen living together in holes or "eel pits". Some eels also live in deeper water on
2490-533: The order Anguilliformes ( / æ ŋ ˈ ɡ w ɪ l ɪ f ɔːr m iː z / ), which consists of eight suborders, 20 families , 164 genera , and about 1000 species . Eels undergo considerable development from the early larval stage to the eventual adult stage and are usually predators . The term "eel" is also used for some other eel-shaped fish, such as electric eels (genus Electrophorus ), swamp eels (order Synbranchiformes ), and deep-sea spiny eels (family Notacanthidae). However, these other clades , with
2573-528: The otic vesicle . 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 1970s, 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 1960s that used the lamprey as
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2656-401: The pharyngeal slits , are openings found between the pharynx or throat. Pharyngeal slits are filter feeding organs that help the movement of water through the mouth and out of these slits when feeding. During the lamprey's larval stage they feed by filter feeding. Once lampreys reach their adult phase they become parasitic on other fish, and these gill slits become very important in aiding in
2739-400: The phylum Chordata , which 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 infraphylum Agnatha or Agnathostomata (both meaning without jaws). The other vertebrate infraphylum is Gnathostomata (jawed mouths) and includes
2822-668: The slender giant moray , which reaches 4 m (13 ft). Eels begin life as flat and transparent larvae , called leptocephali . Eel larvae drift in the sea's surface waters, feeding on marine snow , small particles that float in the water. Eel larvae then metamorphose into glass eels and become elvers before finally seeking out their juvenile and adult habitats. Some individuals of anguillid elvers remains in brackish and marine areas close to coastlines, but most of them enter freshwater where they travel upstream and are forced to climb up obstructions, such as weirs , dam walls, and natural waterfalls. Gertrude Elizabeth Blood found that
2905-412: The "agnatha" Conodonta was indeed jawless, if it would have continued to live, its descendants would still be closer related to e.g. humans than to lampreys, and also contempory it was closer related to the ancestor of humans. Due to such considerations, Agnatha can not be consolidated into a coherent grouping without either removing any non-cyclostomata, or by including all vertebrata thus rendering it into
2988-602: The 11th-century Norman Conquest of England, lampreys were found as far upstream in the River Thames as Petersham . The reduction of pollution in the Thames and River Wear has led to recent sightings in London and Chester-le-Street . 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,
3071-542: The 18 carnivorous species, nine migrate from saltwater to freshwater to breed (some of them also have freshwater populations), and nine live exclusively in freshwater. All non-carnivorous forms are freshwater species. Adults of the non-carnivorous species do not feed; they live on reserves acquired as ammocoetes. Lampreys live mostly in coastal and fresh waters and are found in most temperate regions. Some species (e.g. Geotria australis , Petromyzon marinus , and Entosphenus tridentatus ) travel significant distances in
3154-1071: The 20th century, both names were used indiscriminately, even by the same author in subsequent publications. In the mid-1970s, the ICZN was called upon to fix one name or the other, and after much debate had to resolve the issue by voting. Thus, in 1980, the spelling with a "t" won out, and in 1981, it became official that all higher-level taxa based on Petromyzon have to start with "Petromyzont-". Phylogeny based on Brownstein & Near, 2023. Geotria Gray 1851 (pouched lampreys) Mordacia Gray 1853 (southern topeyed lampreys) Caspiomyzon Berg 1906 Petromyzon Linnaeus 1758 ( Sea lamprey ) Ichthyomyzon Girard 1858 Entosphenus Gill 1863 Tetrapleurodon Creaser & Hubbs 1922 (Mexican lampreys) Western American " Lampetra " Lethenteron Creaser & Hubbs 1922 Eudontomyzon Regan 1911 Lampetra sensu stricto Bonnaterre 1788 (Eastern American and European Lampetra ) Recent studies differ regarding
3237-569: The Carboniferous of France, often considered to be a hagfish , has been found to be a lamprey in some studies. The earliest lamprey with the specialised toothed oral disc typical of modern lampreys is Yanliaomyzon from the Middle Jurassic of China around 163 million years old, which is thought to have had a predatory lifestyle like modern lampreys, and probably had a three stage life cycle including ammocoetes. Mesomyzon from
3320-470: The Early Cretaceous of China, which displays the three stage life cycle with ammocoetes, was found in one study to be more closely related to the family Petromyzonidae than to other living lampreys, though other studies have found it to be outside the group containing all living lampreys. Synapomorphies are certain characteristics that are shared over evolutionary history. Organisms possessing
3403-518: The Old English word for "hedgehog", which is igil (meaning "snake eater"), and perhaps in the egi- of Old High German egidehsa "wall lizard". According to this theory, the name Bellerophon ( Βελλεροφόντης , attested in a variant Ἐλλεροφόντης in Eustathius of Thessalonica ) is also related, translating to "the slayer of the serpent" ( ahihán ). In this theory, the ελλερο-
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3486-650: The Paleobiology Database: Freshwater eels ( unagi ) and marine eels ( conger eel , anago ) are commonly used in Japanese cuisine ; foods such as unadon and unajū are popular, but expensive. Eels are also very popular in Chinese cuisine , and are prepared in many different ways. Hong Kong eel prices have often reached 1000 HKD (128.86 US Dollars) per kg, and once exceeded 5000 HKD per kg. In India , eels are popularly eaten in
3569-728: The Southern Hemisphere. It is thought that most modern lamprey diversity emerged during the Cenozoic, particularly within the last 10–20 million years. The oldest fossil lamprey, Priscomyzon , is known from the latest Devonian of South Africa around 360 million years ago, with other stem-group lampreys, like Pipiscius , Mayomyzon and Hardistiella known from the Carboniferous of North America. These Paleozoic stem-lampreys are small relative to modern lampreys, and while they had well developed oral discs with
3652-610: The World classifies lampreys within the Class Petromyzontida, a taxon called Petromyzonti in Eschmeyer's Catalog of Fishes . 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 of
3735-428: The absence of jaws , modern agnathans are characterised by absence of paired fins ; the presence of a notochord both in larvae and adults; and seven or more paired gill pouches. Lampreys have a light sensitive pineal eye (homologous to the pineal gland in mammals ). All living and most extinct Agnatha do not have an identifiable stomach or any appendages . Fertilization and development are both external. There
3818-472: 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. While the majority of (invertebrate) suspension feeders thrive in waters containing under 1 mg suspended organic solids per litre (<1 mg/L), ammocoetes demand minimum 4 mg/L, with concentrations in their habitats having been measured up to 40 mg/L. During metamorphosis
3901-406: 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 to eat flesh and may even invade the internal organs of the host. Tissue feeders can also involve
3984-564: The body, which pull rather than push their bodies through the water. Different species of lamprey have many shared physical characteristics. The same anatomical structure can serve different functions in the lamprey depending on whether or not it is carnivorous . The mouth and suction capabilities of the lamprey not only allow it to cling to a fish as a parasite , but provide it with limited climbing ability so that it can travel upstream and up ramps or rocks to breed. This ability has been studied in an attempt to better understand how lampreys battle
4067-593: The classes Chondrichthyes (sharks), Osteichthyes (bony fishes), Amphibia , Reptilia , Aves , and Mammalia . Some researchers have classified lampreys as the sole surviving representatives of the Linnean class Cephalaspidomorphi . Cephalaspidomorpha is sometimes given as a subclass of the Cephalaspidomorphi. Fossil evidence now suggests lampreys and cephalaspids acquired their shared characters by convergent evolution . The 5th edition of Fishes of
4150-535: 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. Adults superficially resemble eels in that they have scaleless , elongated bodies, with
4233-492: The continental shelves and over the slopes deep as 4,000 m (13,000 ft). Only members of the Anguilla regularly inhabit fresh water, but they, too, return to the sea to breed. The heaviest true eel is the European conger . The maximum size of this species has been reported as reaching a length of 3 m (10 ft) and a weight of 110 kg (240 lb). Other eels are longer, but do not weigh as much, such as
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#17327806161674316-498: The current and move forward despite only being able to hold onto the rock at a single point. Some scientists are also hoping to design ramps that will optimize the lamprey's climbing ability, as lampreys are valued as food in the Northwest United States and need to travel upstream to reproduce. Many lampreys exhibit countershading , a form of camouflage . Similarly to many other aquatic species, most lampreys have
4399-425: 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 feeders, collecting detritus, algae, and microorganisms. The eyes of the larvae are underdeveloped, but are capable of discriminating changes in illuminance. Ammocoetes can grow from 3–4 inches (8–10 centimetres) to about 8 inches (20 cm). Many species change color during
4482-410: The defining characteristics of a chordate. The notochord provides signaling and mechanical cues to help the organism when swimming. The dorsal nerve cord is another characteristic of lampreys that defines them as chordates. During development this part of the ectoderm rolls creating a hollow tube. This is often why it is referred to as the dorsal "hollow" nerve cord. The third chordate feature, which are
4565-442: The eel fisheries at Ballisodare were greatly improved by the hanging of loosely plaited grass ladders over barriers, enabling elvers to ascend more easily. Several sets of classifications of eels exist; some, such as FishBase which divide eels into 20 families, whereas other classification systems such as ITIS and Systema Naturae 2000 include additional eel families, which are noted below. Genomic studies indicate that there
4648-419: The eggs are fertilized. 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. Taxonomists place lampreys and hagfish in the subphylum Vertebrata of
4731-584: The etymology is uncertain. Lamprey is sometimes seen for the plural form. There are about 38 known extant species of lampreys and around seven known extinct species. They are classified in three families: two small families in the Southern Hemisphere ( Geotriidae , Mordaciidae ) and one large family in the Northern Hemisphere ; ( Petromyzontidae ). Genetic evidence suggests that lampreys are more closely related to hagfish ,
4814-400: The exception of deep-sea spiny eels, whose order Notacanthiformes is the sister clade to true eels, evolved their eel-like shapes independently from the true eels. As a main rule, most eels are marine. Exceptions are the catadromous genus Anguilla and the freshwater moray , which spend most of their life in freshwater, the anadromous rice-paddy eel , which spawns in freshwater, and
4897-918: The family Cyematidae of bobtail snipe eels is included in the Anguilliformes, but in the FishBase system that family is included in the order Saccopharyngiformes . The electric eel of South America is not a true eel but is a South American knifefish more closely related to the carps and catfishes . Phylogeny based on Johnson et al. 2012. Protanguillidae Synaphobranchidae Heterenchelyidae Myrocongridae Muraenidae [REDACTED] Chlopsidae Derichthyidae Nettastomatidae Congridae [REDACTED] Ophichthidae Muraenesocidae Moringuidae Eurypharyngidae Saccopharyngidae [REDACTED] Monognathidae Cyematidae [REDACTED] Nemichthyidae Serrivomeridae Anguillidae [REDACTED] Based on
4980-489: The flesh of their prey to yield blood. The last common ancestor of lampreys appears to have been specialized to feed on the blood and body fluids of other fish after metamorphosis. They attach their mouthparts to the target animal's 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 primarily used to help
5063-425: The freshwater snake eel Stictorhinus . Eels are elongated fish, ranging in length from 5 cm (2 in) in the one-jawed eel ( Monognathus ahlstromi ) to 4 m (13 ft) in the slender giant moray . Adults range in weight from 30 g (1 oz) to well over 25 kg (55 lb). They possess no pelvic fins , and many species also lack pectoral fins . The dorsal and anal fins are fused with
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#17327806161675146-591: The gnathostomes than to the surviving agnathans, known as cyclostomes. Cyclostomes apparently split from other agnathans before the evolution of dentine and bone, which are present in many fossil agnathans, including conodonts . Agnathans declined in the Devonian and never recovered. Approximately 500 million years ago, two types of recombinatorial adaptive immune systems (AISs) arose in vertebrates. The jawed vertebrates diversify their repertoire of immunoglobulin domain-based T and B cell antigen receptors mainly through
5229-468: The highest number of chromosomes (164–174) among vertebrates. Due to certain peculiarities in their adaptive immune system , the study of lampreys provides valuable insight into the evolution of vertebrate adaptive immunity. Generated from a somatic recombination of leucine-rich repeat gene segments, lamprey leukocytes express surface variable lymphocyte receptors (VLRs). This convergently evolved characteristic allows them to have lymphocytes that work as
5312-477: The hypothesis that both groups of living agnathans, hagfishes and lampreys , are more closely related to each other than to jawed fish , forming the clade Cyclostomi . The oldest fossil agnathans appeared in the Cambrian . Living jawless fish comprise about 120 species in total. Hagfish are considered members of the subphylum Vertebrata , because they secondarily lost vertebrae; before this event
5395-426: The jaws of juvenile lampreys, a muscular flap-like structure called the velum is present, which serves to generate a water current towards the mouth opening, which enables feeding and respiration. The unique morphological characteristics of lampreys, such as their cartilaginous skeleton , suggest they are the sister taxon (see cladistics ) of all living jawed vertebrates ( gnathostomes ). They are usually considered
5478-510: 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. In contrast, many species are anadromous and migrate to the sea, beginning to prey on other animals while still swimming downstream after their metamorphosis provides them with eyes, teeth, and
5561-430: The largest species, the sea lamprey having a maximum body length of around 1.2 metres (3.9 ft). Lacking paired fins , adult lampreys have one nostril atop the head and seven gill pores on each side of the head. The brain of the lamprey is divided into the telencephalon , diencephalon , midbrain , cerebellum , and medulla . Lampreys have been described as the only living vertebrates to have four eyes, having
5644-677: The late Cambrian to the Triassic. Many Ordovician, Silurian, and Devonian agnathans were armored with heavy bony-spiky plates. The first armored agnathans—the Ostracoderms , precursors to the bony fish and hence to the tetrapods (including humans )—are known from the middle Ordovician , and by the Late Silurian the agnathans had reached the high point of their evolution. Most of the ostracoderms, such as thelodonts , osteostracans , and galeaspids , were more closely related to
5727-442: The length of its body as an adult. These markings can also sometimes be used to determine what stage of the life cycle the lamprey is in; G. australis individuals lose these stripes when they approach the reproductive phase and begin to travel upstream. Another example is Petromyzon marinus , which shifts to more of an orange color as it reaches the reproductive stage in its life cycle. Northern lampreys ( Petromyzontidae ) have
5810-466: The most basal group of the Vertebrata . Instead of true vertebrae, they have a series of cartilaginous structures called arcualia arranged above the notochord. Hagfish , which 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. The heart of the lamprey
5893-511: The network scheme despite claims by Grillner that the network is characterised (Parker 2006, 2010). 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 . Agnatha Agnatha ( / ˈ æ ɡ n ə θ ə , æ ɡ ˈ n eɪ θ ə / ; from Ancient Greek ἀ- ( a- ) 'without' and γνάθος ( gnáthos ) 'jaws')
5976-466: The only other living group of jawless fish, than they are to jawed vertebrates , forming the superclass Cyclostomi . The oldest fossils of stem-group lampreys are from the latest Devonian Period , around 360 million years ago, with modern looking forms only appearing during the Jurassic Period , around 163 million years ago, with the modern families likely splitting from each sometime between
6059-406: The open ocean, as evidenced by their lack of reproductive isolation between populations. Other species are found in land-locked lakes. 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 by river habitat loss, overfishing and pollution. In Britain, at the time of
6142-486: The parapineal organ. One of the key physical components to the lamprey are the intestines , which are located ventral to the notochord . Intestines aid in osmoregulation by intaking water from its environment and desalinating the water they intake to an iso-osmotic state with respect to blood, and are also responsible for digestion . Studies have shown that lampreys are among the most energy-efficient swimmers. Their swimming movements generate low-pressure zones around
6225-645: The rearrangement of V(D)J gene segments and somatic hypermutation, but none of the fundamental AIS recognition elements in jawed vertebrates have been found in jawless vertebrates. Instead, the AIS of jawless vertebrates is based on variable lymphocyte receptors (VLRs) that are generated through recombinatorial usage of a large panel of highly diverse leucine-rich-repeat (LRR) sequences. Three VLR genes (VLRA, VLRB, and VLRC) have been identified in lampreys and hagfish, and are expressed on three distinct lymphocytes lineages. VLRA+ cells and VLRC+ cells are T-cell-like and develop in
6308-425: The respiration of the organism. The final chordate synapomorphy is the post anal tail, which is muscular and extends behind the anus. Oftentimes adult amphioxus and lamprey larvae are compared by anatomists due to their similarities. Similarities between adult amphioxus and lamprey larvae include a pharynx with pharyngeal slits, a notochord, a dorsal hollow nerve cord and a series of somites that extend anterior to
6391-566: The same region is Haikouella . A possible agnathid that has not been formally described was reported by Simonetti from the Middle Cambrian Burgess Shale of British Columbia . Conodonts , a class of agnathans which arose in the early Cambrian, remained common enough until their extinction in the Triassic that their teeth (the only parts of them that were usually fossilized) are often used as index fossils from
6474-766: The second part of the Latin word for eels, anguilla , attested in its simplex form illa (in a glossary only), and the Greek word for "eel", egkhelys (the second part of which is attested in Hesychius as elyes ). The first compound member, anguis ("snake"), is cognate to other Indo-European words for "snake" (compare Old Irish escung "eel", Old High German unc "snake", Lithuanian angìs , Greek ophis, okhis , Vedic Sanskrit áhi , Avestan aži , Armenian auj, iž , Old Church Slavonic *ǫžь , all from Proto-Indo-European *h₁ogʷʰis ). The word also appears in
6557-438: The teeth on the oral disc in the excision of tissue. As a result, the flesh-feeders have smaller buccal glands as they do not require the production of anticoagulant continuously and mechanisms for preventing solid material entering the branchial pouches, which could otherwise potentially clog the gills. A study of the stomach content of some lampreys has shown the remains of intestines, fins and vertebrae from their prey. Close to
6640-540: The timing of the last common ancestor of all living lampreys, with some suggesting a Middle Jurassic date, around 175 million years ago, while other studies have suggested a younger split, dating to the Late Cretaceous. The older date study posited that the Northern and Southern Hemisphere lampreys diverged as part of the breakup of Pangea , while the Late Cretaceous study suggested that modern lampreys emerged in
6723-874: The town is located. The daylight passage in the spring of elvers upstream along the Thames was at one time called "eel fare". The word 'elver' is thought to be a corruption of "eel fare". A famous attraction on the French Polynesian island of Huahine (part of the Society Islands ) is the bridge across a stream hosting three- to six-foot-long eels, deemed sacred by local culture. Eel fishing in Nazi -era Danzig plays an important role in Günter Grass ' novel The Tin Drum . The cruelty of humans to eels
6806-554: The word for eel can be reconstructed. It may have been *ēl(l)-u- , *ēl(l)-o- , or something similar. The large lake of Almere , which existed in the early Medieval Netherlands , got its name from the eels which lived in its water (the Dutch word for eel is aal or ael , so: " ael mere " = "eel lake"). The name is preserved in the new city of Almere in Flevoland , given in 1984 in memory of this body of water on whose site
6889-479: Was inferred from molecular and developmental data, the Craniata hypothesis was accepted (and is still sometimes used as a strictly morphological descriptor) to reference hagfish plus vertebrates. Agnathans are ectothermic , meaning they do not regulate their own body temperature. Agnathan metabolism is slow in cold water, and therefore they do not have to eat very much. They have no distinct stomach, but rather
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