This taxon is often included in the paraphyletic superclass Agnatha, which also includes several groups of extinct armored fishes called ostracoderms. Most fossil agnathans, such as galeaspids, thelodonts, and osteostracans, are more closely related to vertebrates with jaws (called gnathostomes) than to cyclostomes.[6][7] Cyclostomes seem to have split off before the evolution of dentine and bone, which are present in many fossil agnathans, including conodonts.[8]
Biologists disagree on whether cyclostomes are a clade. The "vertebrate hypothesis" holds that lampreys are more closely related to gnathostomes than they are to the hagfish. The "cyclostome hypothesis", on the other hand, holds that lampreys and hagfishes are more closely related, making cyclostomi monophyletic.[9][10]
Most studies based on anatomy have supported the vertebrate hypothesis,[11] while most molecular phylogenies have supported the cyclostome hypothesis.[2][9][12][13]
There are exceptions in both cases, however. Similarities in the cartilage and muscles of the tongue apparatus also provide evidence of sister-group relationship between lampreys and hagfishes.[14] And at least one molecular phylogeny has supported the vertebrate hypothesis.[15] The embryonic development of hagfishes was once held to be drastically different from that of lampreys and gnathostomes, but recent evidence suggests that it is more similar than previously thought, which may remove an obstacle to the cyclostome hypothesis.[16] There is at present no consensus on the correct topology.
Internal differences and similarities
Both hagfishes and lampreys have a single gonad, but for different reasons. In hagfishes the left gonad degenerates during their ontogeny and only the right gonad develops, whereas in lampreys the left and right gonads fuse into one. There are no gonoducts present.[17][18]
Hagfishes have direct development, but lamprey go through a larval stage followed by metamorphosis into a juvenile form (or adult form in the non-parasitic species). Lamprey larvae live in freshwater and are called ammocoetes, and are the only vertebrates with an endostyle, an organ used for filter feeding that is otherwise found only in tunicates and lancelets. During metamorphosis the lamprey endostyle develops into the thyroid gland.[19]
The cyclostomi evolved oxygen transport hemoglobins independently from the jawed vertebrates.[20]
Hagfishes and lampreys lack a thymus, spleen, myelin and sympathetic chain ganglia.[21][22][23] Neither species has internal eye muscles and hagfishes also lack external eye muscles.[24] Both groups have only a single olfactory organ with a single nostril. The nasal duct ends blindly in a pouch in lampreys but opens into the pharynx in hagfishes. The branchial basket (reduced in hagfishes) is attached to the cranium.[25]
The mouth apparatus in hagfishes and adult lampreys has some similarities, but differ from one another. Lampreys have tooth plates on the top of a tongue-like piston cartilage, and the hagfish have a fixed cartilagous plate on the floor of its mouth with groves that allows tooth plates to slide backwards and forwards over it like a conveyor belt, and are everted as they move over the edge of the plate. Hagfishes also have a keratinous palatine tooth hanging from the roof of the mouth.[26][27]
Unlike jawed vertebrates, which have three semicircular canals in each inner ear, lampreys have only two and hagfishes just one. The semicircular canal of hagfishes contains both stereocilia and a second class of hair cells, apparently a derived trait, whereas lampreys and other vertebrates have stereocilia only. Because the inner ear of hagfishes has two forms of sensory ampullae, their single semicircular canal is assumed to be a result of two semicircular canals that have merged into just one.
The hagfish blood is isotonic with seawater, while lampreys appears to use the same gill-based mechanisms of osmoregulation as marine teleosts. Yet the same mechanisms are apparent in the mitochondria-rich cells in the gill epithelia of hagfishes, but never develops the ability to regulate the blood's salinity, even if they are capable of regulating the ionic concentration of Ca and Mg ions. It has been suggested that the hagfish ancestors evolved from an anadromous or freshwater species that has since adapted to saltwater over a very long time, resulting in higher electrolyte levels in its blood.[28]
The lamprey intestine has a typhlosole that increases the inner surface like the spiral valve does in some jawed vertebrates. The spiral valve in the latter develops by twisting the whole gut, while the lamprey typhlosole is confined to the mucous membrane of the intestines. The mucous membranes of hagfishes have a primitive typhlosole in the form of permanent zigzag ridges. This trait could be a primitive one, since it is also found in some sea squirts such as Ciona.[29] The intestinal epiphelia of lampreys also have ciliated cells, which have not been detected in hagfishes. Because ciliated intestines are also found in Chondrostei, lungfishes and the early stages of some teleosts, it is considered a primitive condition that has been lost in hagfishes.[30]
^The oldest fish in the world lived 500 million years ago | SBS News
^ ab Kuraku, Shigehiro, S. Blair; Ota, Kinya G. & Kuratani, Shigeru (2009b). "Jawless fishes (Cyclostomata)". In S.B. Hedges & S. Kumar (eds.). Timetree of Life. Oxford University Press. pp. 317–319. ISBN978-0-19-953503-3.
^Haeckel (1895). Systematische Phylogenie der Wirbelthiere (Vertebrata). Entwurf einer systematischen Stammesgeschichte (in German). Vol. 3 (1 ed.). Berlin: Georg Reimer. pp. 142–143.
^Duméril, A.M. Constant (1806). Zoologie analytique, ou me´thode naturelle de classification des animaux, Rendue plus facile a l'Aide de Tableaux Synoptiques (in French). Paris: Allais.
^Turner, Susan; Beattie, Joan (2008). "Joan Crockford-Beattie D.Sc." (PDF). Annals of Bryozoology 2: Aspects of the History of Research on Bryozoans. 2: viii, 442.
^ Zhao Wen-Jin; Zhu Min (2007). "Diversification and faunal shift of Siluro-Devonian vertebrates of China". Geological Journal. 42 (3–4): 351–369. doi:10.1002/gj.1072. S2CID 84943412. Archived from the original on 2013-01-05.
^ Sansom, Robert S. (2009). "Phylogeny, classification, & character polarity of the Osteostraci (Vertebrata)". Journal of Systematic Palaeontology. 7: 95–115. doi:10.1017/S1477201908002551. S2CID 85924210.
^ Baker, Clare V.H. (December 2008). "The evolution and elaboration of vertebrate neural crest cells". Current Opinion in Genetics & Development. 18 (6): 536–543. doi:10.1016/j.gde.2008.11.006. PMID 19121930.
^ ab Delabre, Christiane; et al. (2002). "Complete Mitochondrial DNA of the Hagfish, Eptatretus burgeri: The Comparative Analysis of Mitochondrial DNA Sequences Strongly Supports the Cyclostome Monophyly". Molecular Phylogenetics and Evolution. 22 (2): 184–192. doi:10.1006/mpev.2001.1045. PMID 11820840.
^Stock, David; Whitt GS (7 August 1992). "Evidence from 18S ribosomal RNA sequences that lampreys and hagfishes form a natural group". Science. 257 (5071): 787–9. Bibcode:1992Sci...257..787S. doi:10.1126/science.1496398. PMID 1496398.
^ Janvier, Philippe (2003). Early Vertebrates. Oxford University Press. pp. 1–408. ISBN978-0-19-852646-9.
^ Kuraku, Shigehiro; Meyer, Axel & Kuratani, Shigeru (2009a). "Timing of Genome Duplications Relative to the Origin of the Vertebrates: Did Cyclostomes Diverge before, or after?". Molecular Biology and Evolution. 26 (1): 47–59. doi:10.1093/molbev/msn222. PMID 18842688.
^ Heimberg, Alysha M.; Cowper-Sallari, Richard; Sémon, Marie; Donoghue, Philip C. J.; Peterson, Kevin J. (9 November 2010). "microRNAs reveal the interrelationships of hagfish, lampreys, and gnathostomes and the nature of the ancestral vertebrate". PNAS. 107 (45): 19379–19383. doi:10.1073/pnas.1010350107. PMC2984222. PMID 20959416.
^ Yalden, D.M. (1985). "Feeding mechanisms as evidence for cyclostome monophyly". Zoological Journal of the Linnean Society. 84 (3): 291–300. doi:10.1111/j.1096-3642.1985.tb01802.x. Archived from the original on 2013-01-05.
^ Gürsoy, Halil-Cem; Koper, Dorota; Benecke, Bernd-Joachim (May 2000). "The Vertebrate 7S K RNA Separates Hagfish (Myxine glutinosa) and Lamprey (Lampetra fluviatilis)". Journal of Molecular Evolution. 50 (5): 456–464. Bibcode:2000JMolE..50..456G. doi:10.1007/s002390010048. PMID 10824089. S2CID 9970630.
^ Kuratani, Shigeru & Ota, Kinya G. (2008). "Hagfish (Cyclostomata, Vertebrata): searching for the ancestral developmental plan of vertebrates". BioEssays. 30 (2): 167–172. doi:10.1002/bies.20701. PMID 18197595. S2CID 39473712.
^Miyashita, Tetsuto; Coates, Michael I.; Farrar, Robert; Larson, Peter; Manning, Phillip L.; Wogelius, Roy A.; Edwards, Nicholas P.; Anné, Jennifer; Bergmann, Uwe; Palmer, A. Richard; Currie, Philip J. (2019-02-05). "Hagfish from the Cretaceous Tethys Sea and a reconciliation of the morphological–molecular conflict in early vertebrate phylogeny". Proceedings of the National Academy of Sciences. 116 (6): 2146–2151. doi:10.1073/pnas.1814794116. ISSN 0027-8424. PMC6369785. PMID 30670644.
cyclostomi, cyclostomata, redirects, here, order, bryozoans, cyclostomatida, often, referred, cyclostomata, group, vertebrates, that, comprises, living, jawless, fishes, lampreys, hagfishes, both, groups, have, jawless, mouths, with, horny, epidermal, structur. Cyclostomata redirects here For the order of bryozoans see Cyclostomatida Cyclostomi often referred to as Cyclostomata s ɪ k l oʊ ˈ s t ɒ m e t e is a group of vertebrates that comprises the living jawless fishes the lampreys and hagfishes Both groups have jawless mouths with horny epidermal structures that function as teeth called ceratodontes and branchial arches that are internally positioned instead of external as in the related jawed fishes 1 The name Cyclostomi means round mouths 2 3 4 It was named by Joan Crockford Beattie 5 CyclostomiTemporal range Lochkovian Recent 419 2 0 Ma PreꞒ Ꞓ O S D C P T J K Pg NSea lamprey from SwedenScientific classificationKingdom AnimaliaPhylum ChordataInfraphylum AgnathaSuperclass CyclostomiDumeril 1806ClassesMyxini hagfishes Hyperoartia lampreys and kin Contents 1 Possible external relationships 2 Internal differences and similarities 3 Phylogeny 4 ReferencesPossible external relationships EditThis taxon is often included in the paraphyletic superclass Agnatha which also includes several groups of extinct armored fishes called ostracoderms Most fossil agnathans such as galeaspids thelodonts and osteostracans are more closely related to vertebrates with jaws called gnathostomes than to cyclostomes 6 7 Cyclostomes seem to have split off before the evolution of dentine and bone which are present in many fossil agnathans including conodonts 8 Biologists disagree on whether cyclostomes are a clade The vertebrate hypothesis holds that lampreys are more closely related to gnathostomes than they are to the hagfish The cyclostome hypothesis on the other hand holds that lampreys and hagfishes are more closely related making cyclostomi monophyletic 9 10 Most studies based on anatomy have supported the vertebrate hypothesis 11 while most molecular phylogenies have supported the cyclostome hypothesis 2 9 12 13 There are exceptions in both cases however Similarities in the cartilage and muscles of the tongue apparatus also provide evidence of sister group relationship between lampreys and hagfishes 14 And at least one molecular phylogeny has supported the vertebrate hypothesis 15 The embryonic development of hagfishes was once held to be drastically different from that of lampreys and gnathostomes but recent evidence suggests that it is more similar than previously thought which may remove an obstacle to the cyclostome hypothesis 16 There is at present no consensus on the correct topology Internal differences and similarities EditBoth hagfishes and lampreys have a single gonad but for different reasons In hagfishes the left gonad degenerates during their ontogeny and only the right gonad develops whereas in lampreys the left and right gonads fuse into one There are no gonoducts present 17 18 Hagfishes have direct development but lamprey go through a larval stage followed by metamorphosis into a juvenile form or adult form in the non parasitic species Lamprey larvae live in freshwater and are called ammocoetes and are the only vertebrates with an endostyle an organ used for filter feeding that is otherwise found only in tunicates and lancelets During metamorphosis the lamprey endostyle develops into the thyroid gland 19 The cyclostomi evolved oxygen transport hemoglobins independently from the jawed vertebrates 20 Hagfishes and lampreys lack a thymus spleen myelin and sympathetic chain ganglia 21 22 23 Neither species has internal eye muscles and hagfishes also lack external eye muscles 24 Both groups have only a single olfactory organ with a single nostril The nasal duct ends blindly in a pouch in lampreys but opens into the pharynx in hagfishes The branchial basket reduced in hagfishes is attached to the cranium 25 The mouth apparatus in hagfishes and adult lampreys has some similarities but differ from one another Lampreys have tooth plates on the top of a tongue like piston cartilage and the hagfish have a fixed cartilagous plate on the floor of its mouth with groves that allows tooth plates to slide backwards and forwards over it like a conveyor belt and are everted as they move over the edge of the plate Hagfishes also have a keratinous palatine tooth hanging from the roof of the mouth 26 27 Unlike jawed vertebrates which have three semicircular canals in each inner ear lampreys have only two and hagfishes just one The semicircular canal of hagfishes contains both stereocilia and a second class of hair cells apparently a derived trait whereas lampreys and other vertebrates have stereocilia only Because the inner ear of hagfishes has two forms of sensory ampullae their single semicircular canal is assumed to be a result of two semicircular canals that have merged into just one The hagfish blood is isotonic with seawater while lampreys appears to use the same gill based mechanisms of osmoregulation as marine teleosts Yet the same mechanisms are apparent in the mitochondria rich cells in the gill epithelia of hagfishes but never develops the ability to regulate the blood s salinity even if they are capable of regulating the ionic concentration of Ca and Mg ions It has been suggested that the hagfish ancestors evolved from an anadromous or freshwater species that has since adapted to saltwater over a very long time resulting in higher electrolyte levels in its blood 28 The lamprey intestine has a typhlosole that increases the inner surface like the spiral valve does in some jawed vertebrates The spiral valve in the latter develops by twisting the whole gut while the lamprey typhlosole is confined to the mucous membrane of the intestines The mucous membranes of hagfishes have a primitive typhlosole in the form of permanent zigzag ridges This trait could be a primitive one since it is also found in some sea squirts such as Ciona 29 The intestinal epiphelia of lampreys also have ciliated cells which have not been detected in hagfishes Because ciliated intestines are also found in Chondrostei lungfishes and the early stages of some teleosts it is considered a primitive condition that has been lost in hagfishes 30 Phylogeny EditAfter Miyashita et al 2019 31 Haikouella Haikouichthys Myllokunmingia MetasprigginaVertebrata Gnathostomata jawed fish Anaspida Cornovichthys Achanarella Ciderius Birkeniida Lasanius Euphanerops Jamoytius Pipiscius Euconodonta conodonts Cyclostomi MyxinikelaMyxinoidea Tethymyxine tapirostrumRubicundus eosRubicundus lopheliaeMyxine glutinosaNeomyxine biniplicataEptatretus stoutiiEptatretus burgeri Paramyxine spp crown group Gilpichthys Hardistiella Mayomyzon Myxineidus Priscomyzon MesomyzonPetromyzontiformes Geotria australisMordacia mordaxPetromyzon marinusLampetra fluviatilisLethenteron camtschaticum crown group crown group crown group References Edit The oldest fish in the world lived 500 million years ago SBS News a b Kuraku Shigehiro S Blair Ota Kinya G amp Kuratani Shigeru 2009b Jawless fishes Cyclostomata In S B Hedges amp S Kumar eds Timetree of Life Oxford University Press pp 317 319 ISBN 978 0 19 953503 3 Haeckel 1895 Systematische Phylogenie der Wirbelthiere Vertebrata Entwurf einer systematischen Stammesgeschichte in German Vol 3 1 ed Berlin Georg Reimer pp 142 143 Dumeril A M Constant 1806 Zoologie analytique ou me thode naturelle de classification des animaux Rendue plus facile a l Aide de Tableaux Synoptiques in French Paris Allais Turner Susan Beattie Joan 2008 Joan Crockford Beattie D Sc PDF Annals of Bryozoology 2 Aspects of the History of Research on Bryozoans 2 viii 442 Zhao Wen Jin Zhu Min 2007 Diversification and faunal shift of Siluro Devonian vertebrates of China Geological Journal 42 3 4 351 369 doi 10 1002 gj 1072 S2CID 84943412 Archived from the original on 2013 01 05 Sansom Robert S 2009 Phylogeny classification amp character polarity of the Osteostraci Vertebrata Journal of Systematic Palaeontology 7 95 115 doi 10 1017 S1477201908002551 S2CID 85924210 Baker Clare V H December 2008 The evolution and elaboration of vertebrate neural crest cells Current Opinion in Genetics amp Development 18 6 536 543 doi 10 1016 j gde 2008 11 006 PMID 19121930 a b Delabre Christiane et al 2002 Complete Mitochondrial DNA of the Hagfish Eptatretus burgeri The Comparative Analysis of Mitochondrial DNA Sequences Strongly Supports the Cyclostome Monophyly Molecular Phylogenetics and Evolution 22 2 184 192 doi 10 1006 mpev 2001 1045 PMID 11820840 Stock David Whitt GS 7 August 1992 Evidence from 18S ribosomal RNA sequences that lampreys and hagfishes form a natural group Science 257 5071 787 9 Bibcode 1992Sci 257 787S doi 10 1126 science 1496398 PMID 1496398 Janvier Philippe 2003 Early Vertebrates Oxford University Press pp 1 408 ISBN 978 0 19 852646 9 Kuraku Shigehiro Meyer Axel amp Kuratani Shigeru 2009a Timing of Genome Duplications Relative to the Origin of the Vertebrates Did Cyclostomes Diverge before or after Molecular Biology and Evolution 26 1 47 59 doi 10 1093 molbev msn222 PMID 18842688 Heimberg Alysha M Cowper Sallari Richard Semon Marie Donoghue Philip C J Peterson Kevin J 9 November 2010 microRNAs reveal the interrelationships of hagfish lampreys and gnathostomes and the nature of the ancestral vertebrate PNAS 107 45 19379 19383 doi 10 1073 pnas 1010350107 PMC 2984222 PMID 20959416 Yalden D M 1985 Feeding mechanisms as evidence for cyclostome monophyly Zoological Journal of the Linnean Society 84 3 291 300 doi 10 1111 j 1096 3642 1985 tb01802 x Archived from the original on 2013 01 05 Gursoy Halil Cem Koper Dorota Benecke Bernd Joachim May 2000 The Vertebrate 7S K RNA Separates Hagfish Myxine glutinosa and Lamprey Lampetra fluviatilis Journal of Molecular Evolution 50 5 456 464 Bibcode 2000JMolE 50 456G doi 10 1007 s002390010048 PMID 10824089 S2CID 9970630 Kuratani Shigeru amp Ota Kinya G 2008 Hagfish Cyclostomata Vertebrata searching for the ancestral developmental plan of vertebrates BioEssays 30 2 167 172 doi 10 1002 bies 20701 PMID 18197595 S2CID 39473712 Comparative Vertebrate Morphology Morphogenesis Evolutionary Biology Cell Cell Communication and Complex Disease Biologists find that red blooded vertebrates evolved twice independently Phys org Lamprey immunity is far from primitive PNAS Archived from the original on 2021 01 18 Retrieved 2018 05 09 Evolution of Myelin Proteins The Biological Bulletin Vol 207 No 2 The Autonomic Nervous System and Chromaffin Tissue in Hagfishes The Changing Visual System Maturation and Aging in the Central Nervous System Hyman s Comparative Vertebrate Anatomy Biology of the Cyclostomes Hagfish Cronodon Evolutionary Biology of Primitive Fishes microRNAs reveal the interrelationships of hagfish lampreys and gnathostomes and the nature of the ancestral vertebrate PDF Archived from the original PDF on 2016 03 04 Retrieved 2014 04 09 Fish Physiology The Multifunctional Gut of Fish Miyashita Tetsuto Coates Michael I Farrar Robert Larson Peter Manning Phillip L Wogelius Roy A Edwards Nicholas P Anne Jennifer Bergmann Uwe Palmer A Richard Currie Philip J 2019 02 05 Hagfish from the Cretaceous Tethys Sea and a reconciliation of the morphological molecular conflict in early vertebrate phylogeny Proceedings of the National Academy of Sciences 116 6 2146 2151 doi 10 1073 pnas 1814794116 ISSN 0027 8424 PMC 6369785 PMID 30670644 Kerr John Graham 1911 Cyclostomata In Chisholm Hugh ed Encyclopaedia Britannica Vol 7 11th ed Cambridge University Press pp 686 689 Related text and image resources Nelson Joseph S 2006 Fishes of the World John Wiley amp Sons Inc ISBN 0 471 25031 7 Retrieved from https en wikipedia org w index php title Cyclostomi amp oldid 1132081118, wikipedia, wiki, book, books, library,
