Editing Amphibian (section)

== Characteristics ==
The superclass [[Tetrapoda]] is divided into four classes of vertebrate animals with four limbs.<ref>{{cite web |url=http://tolweb.org/Terrestrial_Vertebrates/14952 |title=Terrestrial Vertebrates |author=Laurin, Michel |year=2011 |work=Tree of Life Web Project |access-date=September 16, 2012 |archive-date=March 1, 2011 |archive-url=https://web.archive.org/web/20110301091857/http://tolweb.org/Terrestrial_Vertebrates/14952 |url-status=live }}</ref> Reptiles, birds and mammals are amniotes, the eggs of which are either laid or carried by the female and are surrounded by several membranes, some of which are impervious.<ref>{{cite web |url=http://tolweb.org/Amniota/14990 |title=Amniota |author1=Laurin, Michel |author2=Gauthier, Jacques A. |year=2012 |work=Tree of Life Web Project |access-date=September 16, 2012 |archive-date=June 1, 2020 |archive-url=https://web.archive.org/web/20200601223227/http://tolweb.org/Amniota/14990 |url-status=live }}</ref> Lacking these membranes, amphibians require water bodies for reproduction, although some species have developed various strategies for protecting or bypassing the vulnerable aquatic larval stage.{{sfn | Dorit | Walker | Barnes | 1991 | pp=843–859 }} They are not found in the sea with the exception of one or two frogs that live in [[brackish water]] in [[mangrove]] swamps;<ref>{{cite book |title=Introduction to the Biology of Marine Life |last=Sumich |first=James L. |author2=Morrissey, John F. |year=2004 |publisher=Jones & Bartlett Learning |isbn=978-0-7637-3313-1 |page=171 |url=https://books.google.com/books?id=Y8vTCze3dHgC&q=Amphibians |access-date=October 15, 2020 |archive-date=April 14, 2021 |archive-url=https://web.archive.org/web/20210414082908/https://books.google.com/books?id=Y8vTCze3dHgC&q=Amphibians |url-status=live }}</ref> the [[Anderson's salamander]] meanwhile occurs in brackish or salt water lakes.<ref>{{cite iucn |author=IUCN SSC Amphibian Specialist Group. |year=2015 |errata=2020 |title=''Ambystoma andersoni'' |page=e.T59051A176772780 |doi=10.2305/IUCN.UK.2015-4.RLTS.T59051A176772780.en}}</ref> On land, amphibians are restricted to moist habitats because of the need to keep their skin damp.{{sfn | Dorit | Walker | Barnes | 1991 | pp=843–859 }}

Modern amphibians have a simplified anatomy compared to their ancestors due to [[Neoteny|paedomorphosis]], caused by two evolutionary trends: miniaturization and an unusually large genome, which result in a slower growth and development rate compared to other vertebrates.<ref>{{Cite book|url=https://books.google.com/books?id=eDKEKy5JJbIC&q=%22This+is+related+to+two+evolutionary+trends+in+amphibians%22&pg=PA12|title=The Ecology and Behavior of Amphibians|first=Kentwood D.|last=Wells|date=February 15, 2010|publisher=University of Chicago Press|isbn=9780226893334|via=Google Books|access-date=June 19, 2020|archive-date=June 25, 2020|archive-url=https://web.archive.org/web/20200625180253/https://books.google.no/books?id=eDKEKy5JJbIC&pg=PA12&dq=%22This+is+related+to+two+evolutionary+trends+in+amphibians%22&hl=no&sa=X&ved=0ahUKEwjJzuaj0ozqAhXRmIsKHZs0C3kQ6AEIKzAA#v=onepage&q=%22This+is+related+to+two+evolutionary+trends+in+amphibians%22&f=false|url-status=live}}</ref><ref>{{Cite journal|title=Biological Scaling Problems and Solutions in Amphibians|first1=Daniel L.|last1=Levy|first2=Rebecca|last2=Heald|date=January 20, 2016|journal=Cold Spring Harbor Perspectives in Biology|volume=8|issue=1|pages=a019166|doi=10.1101/cshperspect.a019166|pmid=26261280|pmc=4691792}}</ref> Another reason for their size is associated with their rapid metamorphosis, which seems to have evolved only in the ancestors of Lissamphibia; in all other known lines the development was much more gradual. Because a remodeling of the feeding apparatus means they do not eat during the metamorphosis, the metamorphosis has to go faster the smaller the individual is, so it happens at an early stage when the larvae are still small. (The largest species of salamanders do not go through a metamorphosis.)<ref>{{Cite book|url=https://books.google.com/books?id=0ps6AwAAQBAJ&q=%22Thus%2C+for+the+duration+of+remodeling+to+be+minimized%2C+body+size+must+be+reduced%22&pg=PT351|title=Amphibian Evolution: The Life of Early Land Vertebrates|first=Rainer R.|last=Schoch|date=March 19, 2014|publisher=John Wiley & Sons|isbn=9781118759134|via=Google Books|access-date=July 21, 2020|archive-date=July 25, 2020|archive-url=https://web.archive.org/web/20200725233758/https://books.google.no/books?id=0ps6AwAAQBAJ&pg=PT351&lpg=PT351&dq=%22Thus,+for+the+duration+of+remodeling+to+be+minimized,+body+size+must+be+reduced%22&source=bl&ots=w-dLMiVpU5&sig=ACfU3U0kexTOogu0YUbV8ovHcfueAiLTaA&hl=no&sa=X&ved=2ahUKEwiVwMO4_t7qAhVCyaQKHdEAAT0Q6AEwAHoECAEQAQ#v=onepage&q=%22Thus,+for+the+duration+of+remodeling+to+be+minimized,+body+size+must+be+reduced%22&f=false|url-status=live}}</ref> Amphibians that lay eggs on land often go through the whole metamorphosis inside the egg. An anamniotic terrestrial egg is less than 1 cm in diameter due to diffusion problems, a size which puts a limit on the amount of posthatching growth.<ref>{{Cite journal|url= https://www.academia.edu/1177175|title= The evolution of body size, Cope's rule and the origin of amniotes|journal= Systematic Biology|volume= 53|issue= 4|pages= 594–622|author= Michel Laurin|pmid= 15371249|year= 2004|doi= 10.1080/10635150490445706|doi-access= free|access-date= July 21, 2020|archive-date= July 14, 2021|archive-url= https://web.archive.org/web/20210714103306/https://www.academia.edu/1177175|url-status= live}}</ref>

The smallest amphibian (and vertebrate) in the world is a [[microhylid]] frog from [[New Guinea]] (''[[Paedophryne amauensis]]'') first discovered in 2012. It has an average length of {{cvt|7.7|mm}} and is part of a genus that contains four of the world's ten smallest frog species.<ref>{{cite journal|last1=Rittmeyer|first1=Eric N. |last2=Allison |first2=Allen |last3=Gründler |first3=Michael C. |last4=Thompson |first4=Derrick K. |last5=Austin |first5=Christopher C. |year=2012 |title=Ecological guild evolution and the discovery of the world's smallest vertebrate |journal=PLOS ONE|volume=7 |issue=1 |pages= e29797 |doi=10.1371/journal.pone.0029797 |pmid=22253785 |pmc=3256195|bibcode = 2012PLoSO...729797R |doi-access=free }}</ref> The largest living amphibian is the {{cvt|1.8|m}} [[Chinese giant salamander]] (''Andrias davidianus'')<ref name="Amphibianfacts">{{cite web |url=http://amphibiaweb.org/amphibian/facts.html |title=Amphibian Facts |author1=Nguyen, Brent |author2=Cavagnaro, John |date=July 2012 |publisher=AmphibiaWeb |access-date=November 9, 2012 |archive-date=January 23, 2014 |archive-url=https://web.archive.org/web/20140123044614/http://amphibiaweb.org/amphibian/facts.html |url-status=live }}</ref> but this is a great deal smaller than the largest amphibian that ever existed—the extinct {{convert|9|m|0|abbr=on}} ''[[Prionosuchus]]'', a crocodile-like temnospondyl dating to 270 million years ago from the middle Permian of Brazil.<ref>{{cite journal|author=Price, L. I.|year=1948 |title=Um anfibio Labirinthodonte da formacao Pedra de Fogo, Estado do Maranhao |journal=Boletim |volume=24 |pages=7–32 |publisher=Ministerio da Agricultura, Departamento Nacional da Producao ineral Divisao de Geologia e Mineralogia}}</ref> The largest frog is the African [[Goliath frog]] (''Conraua goliath''), which can reach {{cvt|32|cm}} and weigh {{cvt|3|kg}}.<ref name="Amphibianfacts" />

Amphibians are ectothermic (cold-blooded) vertebrates that do not maintain their body temperature through internal [[Physiology|physiological]] processes. Their [[Basal metabolic rate|metabolic rate]] is low and as a result, their food and energy requirements are limited. In the adult state, they have tear ducts and movable eyelids, and most species have ears that can detect airborne or ground vibrations. They have muscular tongues, which in many species can be protruded. Modern amphibians have fully [[Ossification|ossified]] vertebrae with [[articular processes]]. Their ribs are usually short and may be fused to the vertebrae. Their skulls are mostly broad and short, and are often incompletely ossified. Their skin contains little [[keratin]] and lacks scales, apart from a few fish-like scales in certain caecilians. The skin contains many [[mucous gland]]s and in some species, [[Skin|poison glands]] (a type of granular gland). The hearts of amphibians have three chambers, two [[atrium (heart)|atria]] and one [[ventricle (heart)|ventricle]]. They have a [[urinary bladder]] and nitrogenous waste products are excreted primarily as [[urea]]. Most amphibians lay their eggs in water and have aquatic larvae that undergo metamorphosis to become terrestrial adults. Amphibians breathe by means of a pump action in which air is first drawn into the [[Buccopharyngeal membrane|buccopharyngeal]] region through the nostrils. These are then closed and the air is forced into the lungs by contraction of the throat.{{sfn | Stebbins | Cohen | 1995 | pp=24–25 }} They supplement this with [[gas exchange]] through the skin.{{sfn | Dorit | Walker | Barnes | 1991 | pp=843–859 }}

=== Anura ===
[[File:Red eyed tree frog edit2.jpg|thumb|alt=Red-eyed tree frog|[[Agalychnis callidryas|Red-eyed tree frog]] (''Agalychnis callidryas'') with limbs and feet specialised for climbing]]
The order [[Anura (frog)|Anura]] (from the Ancient Greek ''[[Privative a|a(n)-]]'' meaning "without" and ''oura'' meaning "tail") comprises the frogs and toads. They usually have long hind limbs that fold underneath them, shorter forelimbs, webbed toes with no claws, no tails, large eyes and glandular moist skin.{{sfn | Stebbins | Cohen | 1995 | p=3 }} Members of this order with smooth skins are commonly referred to as frogs, while those with [[wikt:warty|warty]] skins are known as toads. The difference is not a formal one taxonomically and there are numerous exceptions to this rule. Members of the family [[Bufonidae]] are known as the "true toads".<ref>{{cite web |url=http://www.tolweb.org/Bufonidae |title=Bufonidae, True Toads |author1=Cannatella, David |author2=Graybeal, Anna |year=2008 |work=Tree of Life Web Project |access-date=December 1, 2012 |archive-date=June 14, 2020 |archive-url=https://web.archive.org/web/20200614080646/http://www.tolweb.org/Bufonidae |url-status=live }}</ref> Frogs range in size from the {{convert|30|cm|adj=on}} [[Goliath frog]] (''Conraua goliath'') of West Africa<ref>{{cite web |url=http://www.amnh.org/exhibitions/past-exhibitions/frogs-a-chorus-of-colors/frog-fun-facts |title=Frog fun facts |date=January 12, 2010 |publisher=American Museum of Natural History |access-date=August 29, 2012 |archive-date=February 24, 2013 |archive-url=https://web.archive.org/web/20130224074620/http://www.amnh.org/exhibitions/past-exhibitions/frogs-a-chorus-of-colors/frog-fun-facts |url-status=live }}</ref> to the {{convert|7.7|mm|adj=on}} ''[[Paedophryne amauensis]]'', first described in Papua New Guinea in 2012, which is also the smallest known vertebrate.<ref>{{cite news |title=World's smallest frog discovered in Papua New Guinea |author=Challenger, David |url=https://www.cnn.com/2012/01/12/world/asia/new-frogs/index.html |publisher=CNN|date=January 12, 2012 |access-date=August 29, 2012 |url-status=live |archive-url=https://web.archive.org/web/20120420193348/http://articles.cnn.com/2012-01-12/asia/world_asia_new-frogs_1_frog-papua-new-guinea-body-size?_s=PM:ASIA |archive-date=April 20, 2012 |df=mdy-all }}</ref> Although most species are associated with water and damp habitats, some are specialised to live in trees or in deserts. They are found worldwide except for polar areas.<ref name="Collins">{{cite book |title=Reptiles and Amphibians of Britain and Europe |last1=Arnold |first1=Nicholas |last2=Ovenden |first2= Denys |year=2002 |publisher=Harper Collins Publishers |isbn=978-0-00-219318-4 |pages=13–18}}</ref>

Anura is divided into three suborders that are broadly accepted by the scientific community, but the relationships between some families remain unclear. Future [[molecular genetics|molecular]] studies should provide further insights into their evolutionary relationships.<ref>{{cite journal|last=Faivovich| first=J.|author2=Haddad, C. F. B.|author3= Garcia, P. C. A.|author4= Frost, D. R.|author5= Campbell, J. A.|author6= Wheeler, W. C.| title=Systematic review of the frog family Hylidae, with special reference to Hylinae: Phylogenetic analysis and revision| journal=Bulletin of the American Museum of Natural History| volume=294| pages=1–240| doi=10.1206/0003-0090(2005)294[0001:SROTFF]2.0.CO;2| year=2005|citeseerx=10.1.1.470.2967| s2cid=83925199}}</ref> The suborder [[Archaeobatrachia]] contains four families of primitive frogs. These are [[Ascaphidae]], [[Bombinatoridae]], [[Discoglossidae]] and [[Leiopelmatidae]] which have few derived features and are probably paraphyletic with regard to other frog lineages.<ref name="Ford">{{cite journal| last=Ford| first=L. S.| author2=Cannatella, D. C.| year=1993| title=The major clades of frogs| journal=Herpetological Monographs| volume=7| pages=94–117| doi=10.2307/1466954| jstor=1466954 }}</ref> The six families in the more evolutionarily advanced suborder [[Mesobatrachia]] are the [[fossorial]] [[Megophryidae]], [[Pelobatidae]], [[Pelodytidae]], [[Scaphiopodidae]] and [[Rhinophrynidae]] and the obligatorily aquatic [[Pipidae]]. These have certain characteristics that are intermediate between the two other suborders.<ref name="Ford" /> [[Neobatrachia]] is by far the largest suborder and includes the remaining families of modern frogs, including most common species. Approximately 96% of the over 5,000 extant species of frog are neobatrachians.<ref>{{cite journal | last=San Mauro | first=Diego | title=Initial diversification of living amphibians predated the breakup of Pangaea | journal=American Naturalist | volume=165 | pages=590–599 | year=2005 | author2=Vences, Miguel | author3=Alcobendas, Marina | author4=Zardoya, Rafael | author5=Meyer, Axel | doi=10.1086/429523 | issue=5 | pmid=15795855 | bibcode=2005ANat..165..590S | s2cid=17021360 | url=http://nbn-resolving.de/urn:nbn:de:bsz:352-opus-33053 | access-date=November 10, 2016 | archive-date=February 7, 2017 | archive-url=https://web.archive.org/web/20170207031527/http://nbn-resolving.de/urn:nbn:de:bsz:352-opus-33053 | url-status=live }}</ref>

=== Caudata ===
[[File:Cryptobranchus japonicus.jpg|thumb|left|upright|alt=Japanese giant salamander|[[Japanese giant salamander]] <br/>(''Andrias japonicus''), a primitive salamander]]

The order [[Caudata]] (from the Latin ''cauda'' meaning "tail") consists of the salamanders—elongated, low-slung animals that mostly resemble lizards in form. This is a [[Symplesiomorphy|symplesiomorphic trait]] and they are no more closely related to lizards than they are to mammals.<ref>{{cite web |url=http://www.nature.com/scitable/topicpage/trait-evolution-on-a-phylogenetic-tree-relatedness-41936 |title=Trait Evolution on a Phylogenetic Tree: Relatedness, Similarity, and the Myth of Evolutionary Advancement |author=Baum, David |year=2008 |publisher=Nature Education |access-date=December 1, 2012 |archive-date=March 8, 2014 |archive-url=https://web.archive.org/web/20140308191855/http://www.nature.com/scitable/topicpage/trait-evolution-on-a-phylogenetic-tree-relatedness-41936 |url-status=live }}</ref> Salamanders lack claws, have scale-free skins, either smooth or covered with [[tubercle]]s, and tails that are usually flattened from side to side and often finned. They range in size from the [[Chinese giant salamander]] (''Andrias davidianus''), which has been reported to grow to a length of {{convert|1.8|m}},<ref>{{cite web |url=http://amphibiaweb.org/cgi/amphib_query?where-genus=Andrias&where-species=davidianus |title=''Andrias davidianus'' Chinese giant salamander |author=Sparreboom, Max |date=February 7, 2000 |publisher=AmphibiaWeb |access-date=December 1, 2012 |archive-date=December 26, 2012 |archive-url=https://web.archive.org/web/20121226102607/http://amphibiaweb.org/cgi/amphib_query?where-genus=Andrias&where-species=davidianus |url-status=live }}</ref> to the diminutive ''[[Thorius pennatulus]]'' from Mexico which seldom exceeds {{convert|20|mm|1|abbr=on}} in length.<ref>{{cite web |url=http://amphibiaweb.org/cgi/amphib_query?where-genus=Thorius&where-species=pennatulus |title=''Thorius pennatulus'' |author=Wake, David B. |date=November 8, 2000 |publisher=AmphibiaWeb |access-date=August 25, 2012 |archive-date=May 15, 2012 |archive-url=https://web.archive.org/web/20120515190809/http://amphibiaweb.org/cgi/amphib_query?where-genus=Thorius&where-species=pennatulus |url-status=live }}</ref> Salamanders have a mostly [[Laurasia]]n distribution, being present in much of the [[Holarctic]] region of the northern hemisphere. The family [[Plethodontidae]] is also found in Central America and South America north of the [[Amazon basin]];<ref name="Collins" /> South America was apparently invaded from Central America by about the start of the [[Miocene]], 23 million years ago.<ref name="Elmer2013">{{cite journal|last1=Elmer|first1=K. R.|last2=Bonett|first2=R. M.|last3=Wake|first3=D. B.|last4=Lougheed|first4=S. C.|title=Early Miocene origin and cryptic diversification of South American salamanders|journal=BMC Evolutionary Biology|volume= 13|issue=1|date= 2013-03-04|pages= 59|doi= 10.1186/1471-2148-13-59|pmid=23497060|pmc=3602097 |doi-access=free |bibcode=2013BMCEE..13...59E }}</ref> Urodela is a name sometimes used for all the [[extant taxon|extant]] species of salamanders.<ref name="larson">{{Cite journal| last1=Larson | first1=A. | last2=Dimmick | first2=W. | year=1993 | title=Phylogenetic relationships of the salamander families: an analysis of the congruence among morphological and molecular characters | journal=Herpetological Monographs | volume=7 | issue=7 | pages=77–93 | doi =10.2307/1466953 | jstor=1466953}}</ref> Members of several salamander families have become [[Neoteny|paedomorphic]] and either fail to complete their metamorphosis or retain some larval characteristics as adults.{{sfn | Dorit | Walker | Barnes | 1991 | p=852}} Most salamanders are under {{cvt|15|cm}} long. They may be terrestrial or aquatic and many spend part of the year in each habitat. When on land, they mostly spend the day hidden under stones or logs or in dense vegetation, emerging in the evening and night to forage for worms, insects and other invertebrates.<ref name="Collins" />

[[File:Triturus dobrogicus dunai tarajosgőte.jpg|thumb|alt=Danube crested newt|[[Danube crested newt]] <br/>(''Triturus dobrogicus''), an advanced salamander]]

The suborder [[Cryptobranchoidea]] contains the primitive salamanders. A number of fossil cryptobranchids have been found, but there are only three living species, the Chinese giant salamander (''Andrias davidianus''), the [[Japanese giant salamander]] (''Andrias japonicus'') and the [[hellbender]] (''Cryptobranchus alleganiensis'') from North America. These large amphibians retain several larval characteristics in their adult state; gills slits are present and the eyes are unlidded. A unique feature is their ability to feed by suction, depressing either the left side of their lower jaw or the right.<ref name="ADWCrypto">{{cite web | url=http://animaldiversity.ummz.umich.edu/site/accounts/information/Cryptobranchidae.html | title=Cryptobranchidae | author=Heying, Heather | year=2003 | work=Animal Diversity Web | publisher=University of Michigan | access-date=August 25, 2012 | archive-date=October 21, 2012 | archive-url=https://web.archive.org/web/20121021021234/http://animaldiversity.ummz.umich.edu/site/accounts/information/Cryptobranchidae.html | url-status=live }}</ref> The males excavate nests, persuade females to lay their egg strings inside them, and guard them. As well as breathing with lungs, they respire through the many folds in their thin skin, which has [[Capillary|capillaries]] close to the surface.<ref name="EHSAR">{{cite web | url=http://www.fws.gov/midwest/es/soc/amphibians/eahe-sa.pdf | title=Eastern Hellbender Status Assessment Report | author1=Mayasich, J. | author2=Grandmaison, D. | author3=Phillips, C. | date=June 1, 2003 | publisher=U.S. Fish and Wildlife Service | access-date=August 25, 2012 | archive-date=September 4, 2012 | archive-url=https://web.archive.org/web/20120904084224/http://www.fws.gov/midwest/es/soc/amphibians/eahe-sa.pdf | url-status=live }}</ref>

The suborder [[Salamandroidea]] contains the advanced salamanders. They differ from the cryptobranchids by having fused [[Mandible|prearticular bones]] in the lower jaw, and by using internal fertilisation. In salamandrids, the male deposits a bundle of sperm, the [[spermatophore]], and the female picks it up and inserts it into her [[cloaca]] where the sperm is stored until the eggs are laid.<ref name="BritCaudata">{{cite encyclopedia |url=https://www.britannica.com/EBchecked/topic/100353/Caudata |title=Caudata |author=Wake, David B |encyclopedia=Encyclopædia Britannica |access-date=August 25, 2012 |archive-date=May 16, 2013 |archive-url=https://web.archive.org/web/20130516165633/https://www.britannica.com/EBchecked/topic/100353/Caudata |url-status=live }}</ref> The largest family in this group is Plethodontidae, the lungless salamanders, which includes 60% of all salamander species. The [[Family (biology)|family]] [[Salamandridae]] includes the true salamanders and the name "[[newt]]" is given to members of its subfamily [[Pleurodelinae]].{{sfn | Stebbins | Cohen | 1995 | p=3 }}

The third suborder, [[Sirenoidea]], contains the four species of sirens, which are in a single family, [[Sirenidae]]. Members of this order are [[eel]]-like aquatic salamanders with much reduced forelimbs and no hind limbs. Some of their features are primitive while others are derived.<ref>{{cite book |author=Cogger, H. G. |editor=Zweifel, R. G |year=1998 |title=Encyclopedia of Reptiles and Amphibians |publisher= Academic Press |pages= 69–70 |isbn=978-0-12-178560-4}}</ref> Fertilisation is likely to be external as sirenids lack the cloacal glands used by male salamandrids to produce spermatophores and the females lack [[spermatheca]]e for sperm storage. Despite this, the eggs are laid singly, a behaviour not conducive for external fertilisation.<ref name="BritCaudata" />

=== Gymnophiona ===
[[File:Siphonops paulensis02.jpg|thumb|alt=''Siphonops paulensis''|The limbless South American caecilian ''[[Siphonops paulensis]]'']]
The order [[Gymnophiona]] (from the Greek ''gymnos'' meaning "naked" and ''ophis'' meaning "serpent") or Apoda comprises the caecilians. These are long, cylindrical, limbless animals with a snake- or [[Annelid|worm-like]] form. The adults vary in length from 8 to 75 centimetres (3 to 30 inches) with the exception of [[Caecilia thompsoni|Thomson's caecilian]] (''Caecilia thompsoni''), which can reach {{cvt|150|cm}}. A caecilian's skin has a large number of transverse folds and in some species contains tiny embedded dermal scales. It has rudimentary eyes covered in skin, which are probably limited to discerning differences in light intensity. It also has a pair of short [[tentacle]]s near the eye that can be extended and which have [[Somatosensory system|tactile]] and [[Olfaction|olfactory]] functions. Most caecilians live underground in burrows in damp soil, in rotten wood and under plant debris, but some are aquatic.{{sfn| Stebbins| Cohen | 1995 | p=4}} Most species lay their eggs underground and when the larvae hatch, they make their way to adjacent bodies of water. Others brood their eggs and the larvae undergo metamorphosis before the eggs hatch. A few species give birth to live young, nourishing them with glandular secretions while they are in the oviduct.{{sfn | Dorit | Walker | Barnes | 1991 | p=858}} Caecilians have a mostly [[Gondwana]]n distribution, being found in tropical regions of Africa, Asia and Central and South America.<ref name="Britannica">{{cite encyclopedia |url=https://www.britannica.com/EBchecked/topic/29797/Gymnophiona |title=Gymnophiona |author=Duellman, William E. |encyclopedia=Encyclopædia Britannica |access-date=September 30, 2012 |archive-date=January 14, 2012 |archive-url=https://web.archive.org/web/20120114043346/https://www.britannica.com/EBchecked/topic/29797/Gymnophiona |url-status=live }}</ref>