Caecilian

{{Short description|Order of amphibians}} {{About|an order of amphibians|the bishop of Carthage|Caecilianus}} {{Use dmy dates|date=April 2026}} {{cs1 config|name-list-style=vanc|display-authors=6}} {{Automatic taxobox | fossil_range = Late Triassic (Norian) – Present, {{Fossil range|223|0}} | image = Oscaecilia ochrocephala (16983972190).jpg | image_caption = ''Oscaecilia ochrocephala'' (Caeciliidae) | taxon = Gymnophiona | authority = Müller, 1832<ref name=Frost/> | subdivision_ranks = Subgroups | subdivision = *†''Eocaecilia'' * †''Funcusvermis'' * †''Rubricacaecilia'' * †''Chinlestegophis''? * Clade '''Apoda''' Oppel, 1811 ** Caeciliidae ** Chikilidae ** Dermophiidae ** Herpelidae ** Ichthyophiidae ** Grandisoniidae ** Rhinatrematidae ** Scolecomorphidae ** Siphonopidae ** Typhlonectidae | range_map = | range_map_caption = | synonyms = * Gymnophia Rafinesque, 1814 | synonyms_ref = <ref name=Frost>{{cite web |url=http://research.amnh.org/vz/herpetology/amphibia/Amphibia/Gymnophiona |title=Gymnophiona Müller, 1832 |author=Frost, Darrel R. |year=2019 |work=Amphibian Species of the World: an Online Reference. Version 6.0 |publisher=American Museum of Natural History |access-date=11 September 2019 |archive-date=14 November 2014 |archive-url=https://web.archive.org/web/20141114193701/http://research.amnh.org/vz/herpetology/amphibia/Amphibia/Gymnophiona |url-status=live }}</ref> }}

'''Caecilians''' ({{IPAc-en|s|ᵻ|ˈ|s|ɪ|l|i|ə|n}}; {{langnf|la-x-new||italic=no|blind ones}}) are a group of limbless, worm-shaped or snake-shaped amphibians, with either small eyes or no eyes, comprising the order '''Gymnophiona'''. They mostly live hidden in soil or in streambeds, making them some of the least familiar amphibians. Modern caecilians live in the tropics of South and Central America, Africa, and southern Asia. Caecilians feed on small subterranean creatures, such as earthworms. The body is noodle-like and often dark in colour, and the skull is bullet-shaped and strongly built. Caecilian heads have several unique adaptations, such as fused skull and jaw bones, a two-part system of jaw muscles, and chemosensory tentacles between the eyes and nostrils. The skin is slimy, with ringlike markings or grooves, and in some species hides scales underneath.<ref>{{Cite journal |last=Wilkinson |first=Mark |date=2012 |title=Caecilians. |url=https://www.cell.com/current-biology/pdf/S0960-9822(12)00664-1.pdf |journal=Current Biology |volume=22 |issue=17 |pages=R668–R669 |doi=10.1016/j.cub.2012.06.019 |pmid=22974987 |bibcode=2012CBio...22.R668W |archive-date=17 March 2023 |access-date=15 February 2023 |archive-url=https://web.archive.org/web/20230317221334/https://www.cell.com/current-biology/pdf/S0960-9822(12)00664-1.pdf |url-status=live }}</ref>

Modern caecilians are a clade, the order '''Gymnophiona''' {{IPAc-en|,|dZ|I|m|n|@|'|f|ai|@|n|@}} (or '''Apoda''' {{IPAc-en|'|ae|p|@|d|@}}), one of the three living amphibian groups alongside Anura (frogs and toads) and Urodela (salamanders). Gymnophiona is a crown group, encompassing all modern caecilians and all descendants of their last common ancestor. There are more than 220 living species of caecilian classified in 10 families. '''Gymnophionomorpha''' is a recently coined name for the corresponding total group which includes Gymnophiona as well as a few extinct stem-group caecilians (extinct amphibians whose closest living relatives are caecilians but are not descended from any caecilian).<ref name="Santosetal20" /><ref name=":1" /> Some palaeontologists have used the name Gymnophiona for the total group and the old name Apoda for the crown group.<ref name="Evans&SigogneauRussell2001" /> However, Apoda has other even older uses, including as the name of a genus of butterfly, making its use potentially confusing and best avoided. The clade's name 'Gymnophiona' comes from Ancient Greek γυμνος (''gumnos''), meaning "naked", and ὄφις (''óphis''), meaning "snake", as the caecilians were originally thought to be related to snakes and to lack scales.<ref>Wilkinson, M. (2012). Caecilians. Current Biology, 22(17), R668-R669.</ref>

The study of caecilian evolution is complicated by their poor fossil record and specialized anatomy. Genetic evidence and some anatomical details (such as pedicellate teeth) support the idea that frogs, salamanders, and caecilians (collectively known as lissamphibians) are each other's closest relatives. Frogs and salamanders show many similarities to dissorophoids, a group of extinct amphibians in the order Temnospondyli. Caecilians are more controversial; many studies extend dissorophoid ancestry to caecilians. Some studies have instead argued that caecilians descend from extinct lepospondyl or stereospondyl amphibians, contradicting evidence for lissamphibian monophyly (common ancestry). Rare fossils of early gymnophionans, such as ''Eocaecilia'' and ''Funcusvermis'', have helped to test the various conflicting hypotheses for the relationships between caecilians and other living and extinct amphibians.

== Description == [[File:Schwimmwuehle Röntgen.jpg|thumb|X-ray showing the skeleton of ''Typhlonectes'' (Typhlonectidae)]] Caecilians' anatomy is highly adapted for a burrowing lifestyle. In a couple of species, belonging to the primitive genus ''Ichthyophis'', vestigial traces of limbs have been found, and in ''Typhlonectes compressicauda'' the presence of limb buds has been observed during embryonic development, remnants in an otherwise completely limbless body.<ref>{{Cite web |url=https://scienceforecastoa.com/Articles/JA-V1-E1-1003.pdf |title=An Anatomical Feature of Caecilian Amphibians: The Lengthening of the Body and Organs |access-date=25 March 2024 |archive-date=11 April 2024 |archive-url=https://web.archive.org/web/20240411112340/https://scienceforecastoa.com/Articles/JA-V1-E1-1003.pdf |url-status=live }}</ref> This makes the smaller species resemble worms, while the larger species like ''Caecilia thompsoni'', with lengths up to {{convert|1.5|m|ft|0|abbr=on}}, resemble snakes. Their tails are short or absent, and their cloacae are near the ends of their bodies.<ref>{{cite book |last1=Goin |first1=C. J. |last2=Goin |first2=O.B. |last3=Zug |first3=G.W. |year=1978 |title=Introduction to Herpetology |edition=3rd |location=San Francisco |publisher=W.H. Freeman and Company |isbn=978-0-7167-0020-3 |chapter=Order Gymnophiona |page=201 }}</ref><ref>{{cite book |last=Himstedt |first=Werner |title=Die Blindwühlen |isbn=978-3-89432-434-6 |publisher=Westarp Wissenschaften |location=Magdeburg |language=de |year=1996 }}</ref><ref name="Brittanica" />

Except for one lungless species, ''Atretochoana eiselti'',<ref>{{cite web |title=''Atretochoana eiselti'' |url=http://www.nhm.ac.uk/nature-online/species-of-the-day/evolution/atretochoana-eiselti/index.html |access-date=22 February 2012 |publisher=Natural History Museum |archive-date=21 July 2015 |archive-url=https://web.archive.org/web/20150721223319/http://www.nhm.ac.uk/nature-online/species-of-the-day/evolution/atretochoana-eiselti/index.html |url-status=live }}</ref> all caecilians have lungs, but also use their skin or mouths for oxygen absorption. Often, the left lung is much smaller than the right one, an adaptation to body shape that is also found in snakes.<ref name="Mader">{{Cite journal |last=Mader |first=Douglas |date=June 1995 |title=Reptilian Anatomy |journal=Reptiles |volume=3 |issue=2 |pages=84–93 }}</ref>

Their trunk muscles are adapted to pushing their way through the ground, with the vertebral column and its musculature acting as a piston inside the outer layer of the body wall musculature, which is closely attached to the skin.<ref>[https://books.google.com/books?id=eDKEKy5JJbIC&dq=Caecilians+trunk+musculature+band+vertebral+muscles&pg=PA77 The Ecology and Behavior of Amphibians]</ref> By contracting the outer layer of muscles it squeezes the coelom and generates a strong hydrostatic force that lengthens the body.<ref>{{Cite web |url=https://www.cell.com/current-biology/pdf/S0960-9822(12)00664-1.pdf |title=Caecilians - Current Biology |access-date=15 February 2023 |archive-date=17 March 2023 |archive-url=https://web.archive.org/web/20230317221334/https://www.cell.com/current-biology/pdf/S0960-9822(12)00664-1.pdf |url-status=live }}</ref> This muscle system allows the animal to anchor its hind end in position, and force the head forwards, and then pull the rest of the body up to reach it in waves. In water or very loose mud, caecilians instead swim in an eel-like fashion.<ref name="EoR">{{cite book |last=Nussbaum |first=Ronald A. |editor=Cogger, H.G. |editor2=Zweifel, R.G. |year=1998 |title=Encyclopedia of Reptiles and Amphibians |publisher=Academic Press |location=San Diego |pages=52–59 |isbn=978-0-12-178560-4 }}</ref> Caecilians in the family Typhlonectidae are aquatic, and the largest of their kind. The first fossil discovered belonging to an extant family of caecilians, ''Ymboirana acrux'', is from family Typhlonectidae.<ref>{{Cite journal |last=Santos |first=Rodolfo Otávio |last2=Wilkinson |first2=Mark |last3=do Couto Ribeiro |first3=Graziella |last4=Carvalho |first4=Alberto B |last5=Zaher |first5=Hussam |date=1 October 2024 |title=The first fossil record of an aquatic caecilian (Gymnophiona: Typhlonectidae) |url=https://academic.oup.com/zoolinnean/article/doi/10.1093/zoolinnean/zlad188/7513144 |journal=Zoological Journal of the Linnean Society |language=en |volume=202 |issue=2 |doi=10.1093/zoolinnean/zlad188 |issn=0024-4082 }}</ref> The representatives of this family have a fleshy fin running along the rear section of their bodies, which enhances propulsion in water.<ref>{{cite book |last=Piper |first=Ross |year=2007 |title=Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals |publisher=Greenwood Press }}</ref>

=== Skull and senses === Caecilians have small or absent eyes, with only a single known class of photoreceptors, and their vision is limited to dark-light perception.<ref>{{cite journal |last1=Mohun |first1=Samantha M. |last2=Davies |first2=Wayne I.L. |title=The Evolution of Amphibian Photoreception |journal=Frontiers in Ecology and Evolution |volume=7 |date=27 August 2019 |doi=10.3389/fevo.2019.00321 |doi-access=free }}</ref><ref>{{cite journal |first1=S. M. |last1=Mohun |first2=W. L. |last2=Davies |first3=J. K. |last3=Bowmaker |first4=D. |last4=Pisani |first5=W. |last5=Himstedt |first6=D. J. |last6=Gower |first7=D. M. |last7=Hunt |first8=M. |last8=Wilkinson |title=Identification and characterization of visual pigments in caecilians (Amphibia: Gymnophiona), an order of limbless vertebrates with rudimentary eyes |journal=The Journal of Experimental Biology |volume=213 |pages=3586–3592 |year=2010 |doi=10.1242/jeb.045914 |issue=20 |pmid=20889838 |doi-access=free }}</ref> Despite their restricted vision, caecilians display circadian rhythms in response to the photoperiod and tend to demonstrate more surface activity at night.<ref>{{Cite journal |last=Prakash |first=Avanthika |last2=Gower |first2=David J. |last3=Vengot |first3=Ranjith |last4=Kotharambath |first4=Ramachandran |date=30 April 2024 |title=Circadian rhythm and surface activity in soil-dwelling caecilians (Amphibia: Gymnophiona) |url=https://www.nature.com/articles/s41598-024-60533-5 |journal=Scientific Reports |language=en |volume=14 |issue=1 |doi=10.1038/s41598-024-60533-5 |issn=2045-2322 }}</ref> Unlike other modern amphibians (frogs and salamanders), the skull is compact and solid, with few large openings between plate-like cranial bones. The snout is pointed and bullet-shaped, used to force their way through soil or mud. In most species, the mouth is recessed under the head, so that the snout overhangs the mouth.<ref name="Brittanica">{{cite EB1911|wstitle=Caecilia }}</ref>

The bones in the skull are reduced in number compared to prehistoric amphibian species. Caecilians have one of two skull types, stegokrotaphic or zygokrotaphic. In stegokrotaphic skulls the squamosal covers the temporal region and the jaw closing muscles while in zygokrotaphic skulls the squamosal only partially covers the temporal region.<ref>{{Cite journal |last=Kleinteich |first=Thomas |last2=Maddin |first2=Hillary C. |last3=Herzen |first3=Julia |last4=Beckmann |first4=Felix |last5=Summers |first5=Adam P. |date=1 March 2012 |title=Is solid always best? Cranial performance in solid and fenestrated caecilian skulls |url=https://journals.biologists.com/jeb/article/215/5/833/11238/Is-solid-always-best-Cranial-performance-in-solid |journal=Journal of Experimental Biology |language=en |volume=215 |issue=5 |pages=833–844 |doi=10.1242/jeb.065979 |issn=1477-9145 |archive-date=13 November 2024 |access-date=16 January 2026 |archive-url=https://web.archive.org/web/20241113184631/https://journals.biologists.com/jeb/article/215/5/833/11238/Is-solid-always-best-Cranial-performance-in-solid |url-status=live }}</ref> Many bones of the skull are fused together: the maxilla and palatine bones have fused into a maxillopalatine in all living caecilians, and the nasal and premaxilla bones fuse into a nasopremaxilla in some families. Some families can be differentiated by the presence or absence of certain skull bones, such as the septomaxillae, prefrontals, an/or a postfrontal-like bone surrounding the orbit (eye socket). The braincase is encased in a fully integrated compound bone called the os basale, which takes up most of the rear and lower parts of the skull. In skulls viewed from above, a mesethmoid bone may be visible in some species, wedging into the midline of the skull roof.<ref>{{Cite journal |last=Taylor |first=Edward Harrison |date=1969 |title=Skulls of Gymnophiona and their significance in the taxonomy of the group |url=https://www.biodiversitylibrary.org/page/4383846#page/69/mode/1up |journal=The University of Kansas Science Bulletin |volume=48 |issue=15 |pages=585–687 }}</ref><ref name="nine-family" /><ref>{{Cite journal |last1=Marshall |first1=Ashleigh F |last2=Bardua |first2=Carla |last3=Gower |first3=David J |last4=Wilkinson |first4=Mark |last5=Sherratt |first5=Emma |last6=Goswami |first6=Anjali |date=27 March 2019 |title=High-density three-dimensional morphometric analyses support conserved static (intraspecific) modularity in caecilian (Amphibia: Gymnophiona) crania |url=https://academic.oup.com/biolinnean/article/126/4/721/5320147 |journal=Biological Journal of the Linnean Society |language=en |volume=126 |issue=4 |pages=721–742 |doi=10.1093/biolinnean/blz001 |issn=0024-4066 |hdl=2440/123277 |hdl-access=free }}</ref> [[File:Geotrypetes seraphini 81151958.jpg|thumb|Head of ''Geotrypetes seraphini'' (Dermophiidae), showing reduced eyes, nostrils, and small tentacles below the nostrils]] All caecilians have a pair of unique sensory structures, known as tentacles, located on either side of the head between the eyes and nostrils. These are probably used for a second olfactory capability, in addition to the normal sense of smell based in the nose.<ref name="EoR" />

The ringed caecilian (''Siphonops annulatus'') has dental glands that may be homologous to the venom glands of some snakes and lizards. The function of these glands is unknown.<ref>{{Cite journal |last1=Mailho-Fontana |first1=Pedro Luiz |last2=Antoniazzi |first2=Marta Maria |last3=Alexandre |first3=Cesar |last4=Pimenta |first4=Daniel Carvalho |last5=Sciani |first5=Juliana Mozer |last6=Brodie |first6=Edmund D. |last7=Jared |first7=Carlos |date=July 2020 |title=Morphological Evidence for an Oral Venom System in Caecilian Amphibians |journal=iScience |volume=23 |issue=7 |article-number=101234 |doi=10.1016/j.isci.2020.101234 |pmid=32621800 |pmc=7385905 |bibcode=2020iSci...23j1234M |issn=2589-0042 |doi-access=free }}</ref>

The middle ear consists of only the stapes bone and the oval window, which transfer vibrations into the inner ear through a reentrant fluid circuit as seen in some reptiles. Adults of species in the family Scolecomorphidae lack both a stapes and an oval window, making them the only known amphibians missing all the components of a middle ear apparatus.<ref>[https://books.google.com/books?id=UPJcyY7TuiIC&dq=%22Scolecomorphus+species%2C+in+the+monogeneric+family+Scolecomorphidae%22&pg=PA156 Hearing and Sound Communication in Amphibians]</ref>

The lower jaw is specialized in caecilians. Gymnophionans, including extinct species, have only two components of the jaw: the pseudodentary (at the front, bearing teeth) and pseudoangular (at the back, bearing the jaw joint and muscle attachments). These two components are what remains following fusion between a larger set of bones. An additional inset tooth row with up to 20 teeth lies parallel to the main marginal tooth row of the jaw.<ref name="nine-family" />

All but the most primitive caecilians have two sets of muscles for closing the jaw, compared with the single pair found in other amphibians. One set of muscles, the adductors, insert into the upper edge of the pseudoangular in front of the jaw joint. Adductor muscles are commonplace in vertebrates, and close the jaw by pulling upwards and forwards. A more unique set of muscles, the abductors, insert into the rear edge of the pseudoangular below and behind the jaw joint. They close the jaw by pulling backwards and downwards. Jaw muscles are more highly developed in the most efficient burrowers among the caecilians, and appear to help keep the skull and jaw rigid.<ref name="EoR" /><ref>{{Cite journal |last1=Kleinteich |first1=Thomas |last2=Haas |first2=Alexander |last3=Summers |first3=Adam P |date=15 May 2008 |title=Caecilian jaw-closing mechanics: integrating two muscle systems |journal=Journal of the Royal Society Interface |volume=5 |issue=29 |pages=1491–1504 |doi=10.1098/rsif.2008.0155 |pmc=2607354 |pmid=18482905 }}</ref>

=== Skin === [[File:Caecilia pulchraserrana.jpg|thumb|''Caecilia pulchraserrana'' (Caeciliidae) showing the smooth skin typical of caecilians]]

Their skin is smooth and usually dark, but some species have colourful skins. Inside the skin are calcite scales. Because of these scales, the caecilians were once thought to be related to the fossil Stegocephalia, but they are now believed to be a secondary development, and the two groups are most likely unrelated.<ref name=Brittanica /> Scales are absent in the families Scolecomorphidae and Typhlonectidae, except the species ''Typhlonectes compressicauda'' where minute scales have been found in the hinder region of the body.<ref>{{cite journal |doi=10.1016/j.sjbs.2020.06.009 |title=An insight into the skin glands, dermal scales and secretions of the caecilian amphibian Ichthyophis beddomei |year=2020 |last1=Arun |first1=Damodaran |last2=Sandhya |first2=S. |last3=Akbarsha |first3=Mohammad Abdulkader |last4=Oommen |first4=Oommen V. |last5=Divya |first5=Lekha |journal=Saudi Journal of Biological Sciences |volume=27 |issue=10 |pages=2683–2690 |pmid=32994727 |pmc=7499274 |bibcode=2020SJBS...27.2683A }}</ref> The skin also has numerous ring-shaped folds, or annuli, that partially encircle the body, giving them a segmented appearance. Like some other living amphibians, the skin contains glands that secrete a toxin to deter predators.<ref name=EoR /> The skin secretions of ''Siphonops paulensis'' have been shown to have hemolytic properties.<ref>{{cite journal |author1=Elisabeth N. Ferroni Schwartz |author2=Carlos A. Schwartz |author3=Antonio Sebben |title=Occurrence of hemolytic activity in the skin secretion of the caecilian ''Siphonops paulensis'' |journal=Natural Toxins |volume=6 |issue=5 |pages=179–182 |year=1998 |doi=10.1002/(SICI)1522-7189(199809/10)6:5<179::AID-NT20>3.0.CO;2-M |pmid=10398514 }}</ref>

=== Milk provisioning===

Recent research, as documented in the journal ''Science'', has shed light on the behavior of certain species of caecilians. These studies reveal that some caecilians exhibit a phenomenon wherein they provide their hatchlings with a nutrient-rich substance akin to milk, delivered through a maternal vent. Among the species investigated, the oviparous nonmammalian caecilian amphibian ''Siphonops annulatus'' stood out, indicating that the practice of lactation may be more widespread among these creatures than previously thought. As detailed in a 2024 study, researchers collected 16 mothers of the ''Siphonops annulatus'' species from cacao plantations in Brazil's Atlantic Forest and filmed them with their altricial hatchlings in the lab. The mothers remained with their offspring, which suckled on a white, viscous liquid from their cloaca, experiencing rapid growth in their first week. This milk-like substance, rich in fats and carbohydrates, is produced in the mother's oviduct epithelium's hypertrophied glands, similar to mammal milk. The substance was released seemingly in response to tactile and acoustic stimulation by the babies. The researchers observed the hatchlings emitting high-pitched clicking sounds as they approached their mothers for milk, a behavior unique among amphibians. This milk-feeding behavior may contribute to the development of the hatchlings' microbiome and immune system, similar to mammalian young. The presence of milk production in caecilians that lay eggs suggests an evolutionary transition between egg-laying and live birth.<ref>{{Cite news |last=Quaglia |first=Sofia |date=7 March 2024 |title=Bizarre, Wormlike and Oozing Milk for Their Babies |url=https://www.nytimes.com/2024/03/07/science/caecilians-milk-amphibians-worms.html |access-date=11 March 2024 |work=The New York Times |language=en-US |issn=0362-4331 }}</ref><ref>{{Cite journal |last1=Wake |first1=Marvalee H. |date=7 March 2024 |title=Amphibian hatchlings find mother's milk |journal=Science |language=en |volume=383 |issue=1060-1061 (2024) |pages=1060–1061 |doi=10.1126/science.ado2094 |pmid=38452095 |bibcode=2024Sci...383.1060W }}</ref><ref>{{Cite journal |last1=Mailho-Fontana |first1=Pedro L. |last2=Antoniazzi |first2=Marta M. |last3=Coelho |first3=Guilherme R. |last4=Pimenta |first4=Daniel C. |last5=Fernandes |first5=Lígia P. |last6=Kupfer |first6=Alexander |last7=Brodie |first7=Edmund D. |last8=Jared |first8=Carlos |date=8 March 2024 |title=Milk provisioning in oviparous caecilian amphibians |url=https://www.science.org/doi/10.1126/science.adi5379 |journal=Science |language=en |volume=383 |issue=6687 |pages=1092–1095 |doi=10.1126/science.adi5379 |pmid=38452082 |bibcode=2024Sci...383.1092M |issn=0036-8075 |url-access=subscription |archive-date=8 March 2024 |access-date=8 March 2024 |archive-url=https://web.archive.org/web/20240308145257/https://www.science.org/doi/10.1126/science.adi5379 |url-status=live }}</ref>

== Distribution == thumb|265x265px|Current distribution of caecilians (in green) Caecilians are native to wet, tropical regions of Southeast Asia, India, Bangladesh, Nepal<ref>{{cite news |last1=Rathor |first1=Hariharsingh |title=Kutnjema Mareka Jiv Sarpa Hoina |url=http://kantipur.ekantipur.com/news/2016-05-05/20160505123401.html |access-date=5 May 2016 |agency=Kantipur News |publisher=Katipur |date=5 May 2016 |archive-date=22 February 2017 |archive-url=https://web.archive.org/web/20170222071524/http://kantipur.ekantipur.com/news/2016-05-05/20160505123401.html }}</ref> and Sri Lanka, parts of East and West Africa, the Seychelles Islands in the Indian Ocean, Central America, and in northern and eastern South America. In Africa, caecilians are found from Guinea-Bissau (''Geotrypetes'') to southern Malawi (''Scolecomorphus''), with an unconfirmed record from eastern Zimbabwe. They have not been recorded from the extensive areas of tropical forest in central Africa. In South America, they extend through subtropical eastern Brazil well into temperate northern Argentina. They can be seen as far south as Buenos Aires, when they are carried by the flood waters of the Paraná River coming from farther north. Their American range extends north to southern Mexico. The northernmost distribution is of the species ''Ichthyophis sikkimensis'' of northern India. ''Ichthyophis'' is also found in South China and Northern Vietnam. In Southeast Asia, they are found as far east as Java, Borneo, and the southern Philippines, but they have not crossed Wallace's line and are not present in Australia or nearby islands. There are no known caecilians in Madagascar, but their presence in the Seychelles and India has led to speculation on the presence of undiscovered extinct or extant caecilians there.<ref>James D. Gardner, Jean-Claude Rage, The fossil record of lissamphibians from Africa, Madagascar, and the Arabian Plate, Palaeobiodiversity and Palaeoenvironments 96(1):1-52 · March 2016</ref>

In 2021, a live specimen of ''Typhlonectes natans'', a caecilian native to Colombia and Venezuela, was collected from a drainage canal in South Florida. It was the only caecilian ever reported in the wild in the United States, and is considered to be an introduction, perhaps from the wildlife trade. Whether a breeding population has been established in the area is unknown.<ref>{{Cite web |date=3 August 2021 |title=Worm-Like, Limbless Amphibian Known As Caecilians Spotted in Florida For The First Time |url=https://conservation.reefcause.com/worm-like-limbless-amphibian-known-as-caecilians-spotted-in-florida-for-the-first-time/ |access-date=4 August 2021 |website=Conservation.Reefcause.com |language=en-US |archive-date=4 August 2021 |archive-url=https://web.archive.org/web/20210804000347/https://conservation.reefcause.com/worm-like-limbless-amphibian-known-as-caecilians-spotted-in-florida-for-the-first-time/ |url-status=live }}</ref><ref>{{Cite journal |last1=Sheehy |first1=Coleman |last2=Blackburn |first2=David |last3=Kouete |first3=Marcel |last4=Gestring |first4=Kelly |last5=Laurie |first5=Kristin |last6=Prechtel |first6=Austin |last7=Suarez |first7=Eric |last8=Talley |first8=Brooke |date=15 July 2021 |title=First record of a caecilian (order Gymnophiona, Typhlonectes natans) in Florida and in the United States |url=https://journals.ku.edu/reptilesandamphibians/article/view/15629 |journal=Reptiles & Amphibians |language=en |volume=28 |issue=2 |pages=355–357 |doi=10.17161/randa.v28i2.15629 |issn=2332-4961 |doi-access=free }}</ref>

== Taxonomy ==

The name ''caecilian'' derives from the Latin word ''caecus'', meaning "blind", referring to the small or sometimes nonexistent eyes. The name dates back to the taxonomic name of the first species described by Carl Linnaeus, which he named ''Caecilia tentaculata''.<ref name=Brittanica />

There has historically been disagreement over the use of the two primary scientific names for caecilians, Apoda and Gymnophiona. Some palaeontologists prefer to use the name Apoda to refer to the "crown group", that is, the group containing all modern caecilians and extinct members of these modern lineages and the name Gymnophiona to refer to the total group, that is, all caecilians and caecilian-like amphibians that are more closely related to modern groups than to frogs or salamanders. However, Apoda been used for groups of fishes and of sea cucumbers and is the name of a genus of moth, and its continued use in caecilian taxonomy is potentially confusing and unhelpful.

A classification of caecilians by Wilkinson et al. (2011) divided the living caecilians into 9 families containing nearly 200 species.<ref name=nine-family>{{cite journal |last=Wilkinson |first=M. |author2=San Mauro, D. |author3=Sherratt, E. |author4=Gower, D.J. |year=2011 |title=A nine-family classification of caecilians (Amphibia: Gymnophiona) |journal=Zootaxa |volume=2874 |pages=41–64 |url=http://www.mapress.com/zootaxa/2011/f/zt02874p064.pdf |doi=10.11646/zootaxa.2874.1.3 |s2cid=86301415 |archive-date=31 May 2012 |access-date=15 December 2013 |archive-url=https://web.archive.org/web/20120531201710/http://www.mapress.com/zootaxa/2011/f/zt02874p064.pdf |url-status=live }}</ref> In 2012, a tenth caecilian family was newly described, Chikilidae.<ref name=Chiklidae>{{cite journal |last=Kamei |first=R.G. |author2=San Mauro, D. |author3=Gower, D. J. |author4=Van Bocxlaer, I. |author5=Sherratt, E. |author6=Thomas, A. |author7=Babu, S. |author8=Bossuyt, F. |author9=Wilkinson, M. |author10=Biju, S. D. |year=2012 |title=Discovery of a new family of amphibians from Northeast India with ancient links to Africa |journal=Proc. R. Soc. B |volume=279 |issue=1737 |pages=2396–401 |doi=10.1098/rspb.2012.0150 |pmid=22357266 |pmc=3350690 }}</ref><ref>{{cite news |title=New amphibian family found in India |agency=Associated Press |publisher=CBC News |date=21 February 2012 |url=https://www.cbc.ca/news/science/new-amphibian-family-found-in-india-1.1198979 }}</ref> This classification is based on a thorough definition of monophyly based on morphological and molecular evidence,<ref>{{cite journal |last=San Mauro |first=D. |author2=Gower, D. J. |author3=Oommen, O. V. |author4=Wilkinson, M. |author5=Zardoya, R. |year=2004 |title=Phylogeny of caecilian amphibians (Gymnophiona) based on complete mitochondrial genomes and nuclear RAG1 |journal=Molecular Phylogenetics and Evolution |volume=33 |issue=2 |pages=413–427 |doi=10.1016/j.ympev.2004.05.014 |pmid=15336675 |bibcode=2004MolPE..33..413S }}</ref><ref>{{cite journal |last=San Mauro |first=D. |author2=Gower, D. J. |author3=Massingham, T. |author4=Wilkinson, M. |author5=Zardoya, R. |author6=Cotton, J. A. |year=2009 |title=Experimental design in caecilian systematics: phylogenetic information of mitochondrial genomes and nuclear rag1 |journal=Systematic Biology |volume=58 |issue=4 |pages=425–438 |doi=10.1093/sysbio/syp043 |pmid=20525595 |citeseerx=10.1.1.577.2856 }}</ref><ref>{{cite journal |last=Zhang |first=P. |author2=Wake, M. H. |year=2009 |title=A mitogenomic perspective on the phylogeny and biogeography of living caecilians (Amphibia: Gymnophiona) |journal=Molecular Phylogenetics and Evolution |volume=53 |issue=2 |pages=479–491 |doi=10.1016/j.ympev.2009.06.018 |pmid=19577653 |bibcode=2009MolPE..53..479Z }}</ref><ref>{{cite journal |last=San Mauro |first=D. |author2=Gower, D. J. |author3=Cotton, J. A. |author4=Zardoya, R. |author5=Wilkinson, M. |author6=Massingham, T. |year=2012 |title=Experimental design in phylogenetics: testing predictions from expected information |journal=Systematic Biology |volume=61 |issue=4 |pages=661–674 |doi=10.1093/sysbio/sys028 |pmid=22328568 |doi-access=free }}</ref> and it solves the longstanding problems of paraphyly of the Caeciliidae in previous classifications without an exclusive reliance upon synonymy.<ref name=nine-family /><ref>{{cite journal |last1=Frost |year=2006 |title=The Amphibian Tree of Life |journal=Bulletin of the American Museum of Natural History |volume=297 |pages=1–370, appendices |doi=10.1206/0003-0090(2006)297[0001:TATOL]2.0.CO;2 |first1=Darrel R. |last2=Grant |first2=Taran |last3=Faivovich |first3=Julián |last4=Bain |first4=Raoul H. |last5=Haas |first5=Alexander |last6=Haddad |first6=Célio F.B. |last7=De Sá |first7=Rafael O. |last8=Channing |first8=Alan |last9=Wilkinson |first9=Mark|last10=Donnellan|first10=Stephen C. |last11=Raxworthy |first11=Christopher J. |last12=Campbell |first12=Jonathan A. |last13=Blotto |first13=Boris L. |last14=Moler |first14=Paul |last15=Drewes |first15=Robert C. |last16=Nussbaum |first16=Ronald A. |last17=Lynch |first17=John D. |last18=Green |first18=David M. |last19=Wheeler |first19=Ward C. |s2cid=86140137 |issn=0003-0090 |doi-access=free }}</ref> There are 219 species of caecilian in 33 genera and 10 families.

{|class="wikitable" |- ! style="background:#f0f0f0;"|Family ! style="background:#f0f0f0;"|Image ! style="background:#f0f0f0;"|Taxon author ! style="background:#f0f0f0;"|Genera ! style="background:#f0f0f0;"|Species ! style="background:#f0f0f0;"|Common name ! style="background:#f0f0f0;"|Geographic range |- |Caeciliidae | style="text-align:center;"|140px ''Caecilia subnigricans'' |Rafinesque, 1814 | style="text-align:center;"|2 | style="text-align:center;"|47 |Common caecilians |Central and South America (Bolivia north to Costa Rica). |- |Chikilidae | style="text-align:center;"| |Kamei et al., 2012 | style="text-align:center;"|1 | style="text-align:center;"|4 |Northeast Indian caecilians |Northeast India and Bangladesh, with possible occurrences in Myanmar. |- |Dermophiidae | style="text-align:center;"|140px ''Geotrypetes seraphini'' |Taylor, 1969 | style="text-align:center;"|4 | style="text-align:center;"|15 |Neotropical caecilians |Equatorial Africa (West Africa, Tanzania, Kenya), Central and South America (Colombia north to Mexico). |- |Grandisoniidae (formerly Indotyphlidae) | style="text-align:center;"|140px ''Grandisonia sechellensis'' |Lescure, Renous & Gasc, 1986 | style="text-align:center;"|7 | style="text-align:center;"|24 |Indo-African caecilians |Equatorial Africa (Cameroon, Ethiopia), the Seychelles, western India (Western Ghats). |- |Herpelidae | style="text-align:center;"|140px ''Boulengerula taitana'' |Laurent, 1984 | style="text-align:center;"|2 | style="text-align:center;"|10 |African caecilians |Equatorial Africa (Nigeria south to the Democratic Republic of the Congo, Kenya south to Malawi, possible occurrences in Angola and Zambia). |- |Ichthyophiidae | style="text-align:center;"|140px ''Ichthyophis kodaguensis'' |Taylor, 1969 | style="text-align:center;"|2 | style="text-align:center;"|57 |Asian tailed caecilians |South and Southeast Asia (western India north to Nepal, east to the Philippines, southern China and Indonesia). |- |Rhinatrematidae | style="text-align:center;"|140px ''Epicrionops'' sp. |Nussbaum, 1977 | style="text-align:center;"|3 | style="text-align:center;"|14 |American tailed caecilians |Northern South America (northernmost Brazil west to Venezuela, Colombia, Ecuador, and Peru). |- |Scolecomorphidae | style="text-align:center;"|140px ''Scolecomorphus kirkii'' |Taylor, 1969 | style="text-align:center;"|2 | style="text-align:center;"|6 |Buried-eyed caecilians |Equatorial Africa (Cameroon, Tanzania, Malawi, Mozambique). |- |Siphonopidae | style="text-align:center;"|140px ''Microcaecilia dermatophaga'' |Bonaparte, 1850 | style="text-align:center;"|5 | style="text-align:center;"|28 |South American caecilians |South America (Colombia south to northern Argentina, Paraguay, and southernmost Brazil). |- |Typhlonectidae | style="text-align:center;"|140px ''Typhlonectes natans'' |Taylor, 1968 | style="text-align:center;"|5 | style="text-align:center;"|14 |Aquatic caecilians |South America (Colombia and Venezuela south to northern Argentina and Uruguay). |}

The most recent phylogeny of caecilians is based on molecular mitogenomic evidence examined by San Mauro et al. (2014), and modified to include some more recently described genera such as ''Amazops''.<ref>{{cite journal |author1=Pyron, R.A. |author2=Wiens, J.J. |year=2011 |title=A large-scale phylogeny of Amphibia including over 2800 species, and a revised classification of extant frogs, salamanders, and caecilians |journal=Molecular Phylogenetics and Evolution |volume=61 |issue=2 |pages=543–583 |doi=10.1016/j.ympev.2011.06.012 |pmid=21723399 |doi-access=free |bibcode=2011MolPE..61..543A }}</ref><ref>{{cite journal |last=San Mauro |first=D. |author2=Gower, D. J. |author3=Müller, H. |author4=Loader, S. P. |author5=Zardoya, R. |author6=Nussbaum, R. A. |author7=Wilkinson, M. |year=2014 |title=Life-history evolution and mitogenomic phylogeny of caecilian amphibians |journal=Molecular Phylogenetics and Evolution |volume=73 |pages=177–89 |doi=10.1016/j.ympev.2014.01.009 |pmid=24480323 |bibcode=2014MolPE..73..177S |hdl=10261/123960 |hdl-access=free }}</ref><ref>{{Cite web |title=AmphibiaWeb - Amazops amazops |url=https://amphibiaweb.org/cgi/amphib_query?where-genus=Amazops&where-species=amazops |access-date=24 January 2021 |website=amphibiaweb.org |archive-date=16 May 2021 |archive-url=https://web.archive.org/web/20210516191531/https://amphibiaweb.org/cgi/amphib_query?where-genus=Amazops&where-species=amazops |url-status=live }}</ref>

{{Clade| style=font-size:80%;line-height:80% |label1='''Gymnophiona''' |1={{clade |label1=Eocaeciliidae |1=†''Eocaecilia micropodia'' |2={{clade |1=†''Rubricacaecilia monbaroni'' |label2='''Apoda''' |2={{clade |label1=Rhinatrematidae |1={{clade |1=''Amazops'' |2={{clade |1=''Rhinatrema'' |2=''Epicrionops'' }} }} |label2=Stegokrotaphia |2={{clade |label1=Ichthyophiidae |1={{clade |1=''Uraeotyphlus'' |2=''Ichthyophis'' }} |label2=Teresomata |2={{clade |label1=Scolecomorphidae |1={{clade |1=''Crotaphatrema'' |2=''Scolecomorphus'' }} |label2= |2={{clade |label1= |1={{clade |label1=Chikilidae |1=''Chikila'' |label2=Herpelidae |2={{clade |1=''Herpele'' |2=''Boulengerula'' }} }} |label2= |2={{clade |label1=Caeciliidae |1={{clade |1=?''Atretochoana'' |2=?''Nectocaecilia'' |3=?''Potamotyphlus'' |4=''Chthonerpeton'' |5={{clade |1=''Typhlonectes'' |2={{clade |1=''Oscaecilia'' |2=''Caecilia'' }} }} }} |label2= |2={{clade |label1=Grandisoniidae |1={{clade |1=?''Idiocranium'' |2=?''Indotyphlus'' |3=?''Sylvacaecilia'' |4=''Gegeneophis'' |5={{clade |1=''Hypogeophis'' |2={{clade |1=''Praslinia'' |2=''Grandisonia'' }} }} }} |2={{clade |label1=Dermophiidae |1={{clade |1=''Geotrypetes'' |2={{clade |1=''Schistometopum'' |2={{clade |1=''Gymnopis'' |2=''Dermophis'' }} }} }} |label2=Siphonopidae |2={{clade |1=?''Brasilotyphlus'' |2=?''Microcaecilia'' |3=?''Mimosiphonops'' |4=''Luetkenotyphlus'' |5=''Siphonops'' }} }} }} }} }} }} }} }} }} }} }}

== Evolution == [[File:Eocaecilia BW.jpg|thumb|''Eocaecilia'', an Early Jurassic amphibian commonly considered one of the oldest (stem-group) caecilians]] Little is known of the evolutionary history of the caecilians, which have left a very sparse fossil record. The first fossil, a vertebra dated to the Paleocene, was not discovered until 1972.<ref>{{cite journal |title=The First Fossil Record of Caecilian Amphibians |journal=Nature |volume=239 |issue=5369 |pages=228–231 |last=Estes |first=Richard |author2=Wake, Marvalee H. |date=22 September 1972 |doi=10.1038/239228b0 |bibcode=1972Natur.239..228E |s2cid=4260251 }}</ref> Other vertebrae, which have characteristic features unique to modern species, were later found in Paleocene and Late Cretaceous (Cenomanian) sediments.<ref name=Evans&SigogneauRussell2001>{{cite journal |doi=10.1111/1475-4983.00179 |title=A stem-group caecilian (Lissamphibia: Gymnophiona) from the Lower Cretaceous of North Africa |journal=Palaeontology |volume=44 |issue=2 |pages=259–273 |year=2001 |last1=Evans |first1=Susan E. |last2=Sigogneau-Russell |first2=Denise |doi-access=free |bibcode=2001Palgy..44..259E }}</ref>

Phylogenetic evidence suggests that the ancestors of caecilians and batrachians (including frogs and salamanders) diverged from one another during the Carboniferous. This leaves a gap of more than 70 million years between the presumed origins of caecilians and the earliest definitive fossils of stem-caecilians.<ref name=":0">{{Cite journal |last1=Pardo |first1=Jason D. |last2=Small |first2=Bryan J. |last3=Huttenlocker |first3=Adam K. |date=3 July 2017 |title=Stem caecilian from the Triassic of Colorado sheds light on the origins of Lissamphibia |journal=Proceedings of the National Academy of Sciences |language=en |volume=114 |issue=27 |pages=E5389–E5395 |doi=10.1073/pnas.1706752114 |issn=0027-8424 |pmc=5502650 |pmid=28630337 |doi-access=free |bibcode=2017PNAS..114E5389P }}</ref><ref name=":1" />

Prior to 2023, the earliest fossil attributed to a stem-caecilian (an amphibian closer to caecilians than to frogs or salamanders but not a member of the extant caecilian lineage) comes from the Jurassic period. This primitive genus, ''Eocaecilia'', had small limbs and well-developed eyes.<ref>{{cite journal |title=An Early Jurassic caecilian with limbs |journal=Nature |volume=365 |issue=6443 |pages=246–250 |last=Jenkins |first=Parish A. |author2=Walsh, Denis M. |date=16 September 1993 |doi=10.1038/365246a0 |bibcode=1993Natur.365..246J |s2cid=4342438 }}</ref> In their 2008 description of the Early Permian amphibian ''Gerobatrachus'',<ref>{{cite journal |last1=Anderson |year=2008 |title=A stem batrachian from the Early Permian of Texas and the origin of frogs and salamanders |journal=Nature |doi=10.1038/nature06865 |first1=Jason S. |last2=Reisz |first2=Robert R. |last3=Scott |first3=Diane |last4=Fröbisch |first4=Nadia B. |last5=Sumida |first5=Stuart S. |volume=453 |issue=7194 |pages=515–8 |pmid=18497824 |bibcode=2008Natur.453..515A |s2cid=205212809 }}</ref> Anderson and co-authors suggested that caecilians arose from the Lepospondyl group of ancestral tetrapods, and may be more closely related to amniotes than to frogs and salamanders, which arose from Temnospondyl ancestors. Numerous groups of lepospondyls evolved reduced limbs, elongated bodies, and burrowing behaviors, and morphological studies on Permian and Carboniferous lepospondyls have placed the early caecilian (''Eocaecilia'') among these groups.<ref>{{cite journal |last=Huttenlocker |first=A. K. |author2=Pardo, J. D. |author3=Small, B. J. |author4=Anderson, J. S. |year=2013 |title=Cranial morphology of recumbirostrans (Lepospondyli) from the Permian of Kansas and Nebraska, and early morphological evolution inferred by micro-computed tomography |journal=Journal of Vertebrate Paleontology |volume=33 |issue=3 |pages=540–552 |doi=10.1080/02724634.2013.728998 |bibcode=2013JVPal..33..540H |s2cid=129144343 }}</ref> Divergent origins of caecilians and other extant amphibians may help explain the slight discrepancy between fossil dates for the origins of modern Amphibia, which suggest Permian origins, and the earlier dates, in the Carboniferous, predicted by some molecular clock studies of DNA sequences. Most morphological and molecular studies of extant amphibians, however, support monophyly for caecilians, frogs, and salamanders, and the most recent molecular study based on multi-locus data suggest a Late Carboniferous–Early Permian origin of extant amphibians.<ref>{{cite journal |last=San Mauro |first=D. |year=2010 |title=A multilocus timescale for the origin of extant amphibians |journal=Molecular Phylogenetics and Evolution |volume=56 |pages=554–561 |doi=10.1016/j.ympev.2010.04.019 |pmid=20399871 |issue=2 |bibcode=2010MolPE..56..554S }}</ref>

''Chinlestegophis'', a stereospondyl temnospondyl from the Late Triassic Chinle Formation of Colorado, was proposed to be a stem-caecilian in a 2017 paper by Pardo and co-authors. If confirmed, this would bolster the proposed pre-Triassic origin of Lissamphibia suggested by molecular clocks. It would fill a gap in the fossil record of early caecilians and suggest that stereospondyls as a whole qualify as stem-group caecilians.<ref name=":0" /> However, affinities between ''Chinlestegophis'' and gymnophionans have been disputed along several lines of evidence. A 2020 study questioned the choice of characters supporting the relationship,<ref name="Santosetal20">{{Cite journal |last1=Santos |first1=Rodolfo Otávio |last2=Laurin |first2=Michel |last3=Zaher |first3=Hussam |date=2020 |title=A review of the fossil record of caecilians (Lissamphibia; Gymnophionomorpha) with comments on its use to calibrate molecular timetrees |journal=Biological Journal of the Linnean Society |volume=131 |issue=4 |pages=737–755 |doi=10.1093/biolinnean/blaa148 |doi-access=free }}</ref> and a 2019 reanalysis of the original data matrix found that other equally parsimonious positions were supported for the placement of ''Chinlestegophis'' and gymnophionans among tetrapods.<ref>{{Cite journal |last1=Marjanović |first1=David |last2=Laurin |first2=Michel |date=2019 |title=Phylogeny of Paleozoic limbed vertebrates reassessed through revision and expansion of the largest published relevant data matrix |journal=PeerJ |volume=6 |article-number=e5565 |doi=10.7717/peerj.5565 |pmid=30631641 |pmc=6322490 |doi-access=free }}</ref> In 2024, ''Chinlestegophis'' was consistently recovered as a sister taxon of ''Rileymillerus'' within various positions of Stereospondyli outside Lissamphibia based on phylogenetic analyses and revisions.<ref>{{Cite journal |last1=Marjanović |first1=David |last2=Maddin |first2=Hillary C. |last3=Olori |first3=Jennifer C. |last4=Laurin |first4=Michel |date=4 January 2024 |title=The new problem of ''Chinlestegophis'' and the origin of caecilians (Amphibia, Gymnophionomorpha) is highly sensitive to old problems of sampling and character construction |url=https://fr.pensoft.net/article/109555/ |journal=Fossil Record |volume=27 |issue=1 |pages=55–94 |doi=10.3897/fr.27.e109555 |doi-access=free |bibcode=2024FossR..27...55M }}</ref>

A 2023 paper by Kligman and co-authors described ''Funcusvermis'', another amphibian from the Chinle Formation of Arizona. ''Funcusvermis'' was strongly supported as a stem group caecilian based on traits of its numerous skull and jaw fragments, the largest sample of caecilian fossils known. The paper discussed the various hypotheses for caecilian origins: the polyphyly hypothesis (caecilians as lepospondyls, and other lissamphibians as temnospondyls), the lepospondyl hypothesis (lissamphibians as lepospondyls), and the newer hypothesis supported by ''Chinlestegophis'', where caecilians and other lissamphibians had separate origins within temnospondyls. Nevertheless, all of these ideas were refuted, and the most strongly supported hypothesis combined lissamphibians into a monophyletic group of dissorophoid temnospondyls closely related to ''Gerobatrachus''.<ref name=":1">{{Cite journal |last1=Kligman |first1=Ben T. |last2=Gee |first2=Bryan M. |last3=Marsh |first3=Adam D. |last4=Nesbitt |first4=Sterling J. |last5=Smith |first5=Matthew E. |last6=Parker |first6=William G. |last7=Stocker |first7=Michelle R. |date=25 January 2023 |title=Triassic stem caecilian supports dissorophoid origin of living amphibians |journal=Nature |volume=614 |issue=7946 |language=en |pages=102–107 |doi=10.1038/s41586-022-05646-5 |pmid=36697827 |pmc=9892002 |bibcode=2023Natur.614..102K |issn=1476-4687 }}</ref>

== Behavior ==

=== Reproduction === [[File:CaecilianNHM.png|thumb|upright=1.8|Maternal care in ''Ichthyophis'' (Ichthyophiidae)]] Caecilians are the only order of amphibians to use internal insemination exclusively (although most salamanders have internal fertilization and the tailed frog in the US uses a tail-like appendage for internal insemination in its fast-flowing water environment).<ref name=EoR /> The male caecilians have a long tube-like intromittent organ, the phallodeum,<ref name="Jamieson2006">{{cite book |first=Barrie G. M. |last=Jamieson |title=Reproductive Biology and Phylogeny of Gymnophiona: Caecilians |url=https://books.google.com/books?id=a0hZDwAAQBAJ |year=2006 |publisher=CRC Press |isbn=978-1-4822-8014-2 }}</ref> which is inserted into the cloaca of the female for two to three hours. About 25% of the species are oviparous (egg-laying); the eggs are laid in terrestrial nests rather than in water and are guarded by the female. For some species, the young caecilians are already metamorphosed when they hatch; others hatch as larvae. The larvae are not fully aquatic, but spend the daytime in the soil near the water.<ref name=EoR /><ref>{{Cite web |url=https://www.cell.com/current-biology/pdf/S0960-9822(12)00664-1.pdf |title=Caecilians - Cell Press |access-date=15 February 2023 |archive-date=17 March 2023 |archive-url=https://web.archive.org/web/20230317221334/https://www.cell.com/current-biology/pdf/S0960-9822(12)00664-1.pdf |url-status=live }}</ref>

About 75% of caecilians are viviparous, meaning they give birth to already-developed offspring. The foetus is fed inside the female with cells lining the oviduct, which they eat with special scraping teeth. Some larvae, such as those of ''Typhlonectes'', are born with enormous external gills which are shed almost immediately. left|thumb|''Microcaecilia dermatophaga'' (Siphonopidae) mother and hatchlings. This species is one of several caecilians in which maternal dermatophagy has been observed. The egg-laying herpelid species ''Boulengerula taitana'' feeds its young by developing an outer layer of skin, high in fat and other nutrients, which the young peel off with modified teeth. This allows them to grow by up to 10 times their own weight in a week. The skin is consumed every three days, the time it takes for a new layer to grow, and the young have only been observed to eat it at night. It was formerly thought that the juveniles subsisted only on a liquid secretion from their mothers.<ref name="Kupfer">{{cite journal |journal=Nature |last1=Kupfer |first1=Alex |last2=Muller |first2=Hendrik |last3=Antoniazzi |first3=Marta M. |last4=Jared |first4=Carlos |last5=Greven |first5=Hartmut |last6=Nussbaum |first6=Ronald A. |last7=Wilkinson |first7=Mark |title=Parental investment by skin feeding in a caecilian amphibian |year=2006 |volume=440 |issue=7086 |pages=926–929 |doi=10.1038/nature04403 |pmid=16612382 |bibcode=2006Natur.440..926K |url=https://deepblue.lib.umich.edu/bitstream/2027.42/62957/1/nature04403.pdf |hdl=2027.42/62957 |s2cid=4327433 |hdl-access=free |archive-date=27 April 2024 |access-date=3 September 2019 |archive-url=https://web.archive.org/web/20240427173723/https://deepblue.lib.umich.edu/bitstream/2027.42/62957/1/nature04403.pdf |url-status=live }}</ref><ref>{{cite news |last=Vince |first=Gaia |title='Yummy mummy' worms feed their skin to offspring |newspaper=New Scientist |date=12 April 2006 |url=https://www.newscientist.com/article/dn8988-yummy-mummy-worms-feed-their-skin-to-offspring.html |archive-date=31 May 2015 |access-date=25 August 2017 |archive-url=https://web.archive.org/web/20150531173751/http://www.newscientist.com/article/dn8988-yummy-mummy-worms-feed-their-skin-to-offspring.html |url-status=live }}</ref><ref>{{Cite journal |last1=Kupfer |first1=Alexander |last2=Wilkinson |first2=Mark |last3=Gower |first3=David J. |last4=Müller |first4=Hendrik |last5=Jehle |first5=Robert |date=2008 |title=Care and parentage in a skin-feeding caecilian amphibian |url=https://onlinelibrary.wiley.com/doi/10.1002/jez.475 |journal=Journal of Experimental Zoology Part A: Ecological Genetics and Physiology |language=en |volume=309A |issue=8 |pages=460–467 |doi=10.1002/jez.475 |pmid=18618577 |bibcode=2008JEZA..309..460K |url-access=subscription |archive-date=6 November 2022 |access-date=26 January 2023 |archive-url=https://web.archive.org/web/20221106063140/https://onlinelibrary.wiley.com/doi/10.1002/jez.475 |url-status=live }}</ref> This form of parental care, known as maternal dermatophagy, has also been reported in two species in the family Siphonopidae: ''Siphonops annulatus'' and ''Microcaecilia dermatophaga''. Siphonopids and herpelids are not closely related to each other, having diverged in the Cretaceous Period. The presence of maternal dermatophagy in both families suggest that it may be more widespread among caecilians than previously considered.<ref>{{Cite journal |last1=Wilkinson |first1=Mark |last2=Kupfer |first2=Alexander |last3=Marques-Porto |first3=Rafael |last4=Jeffkins |first4=Hilary |last5=Antoniazzi |first5=Marta M |last6=Jared |first6=Carlos |date=11 June 2008 |title=One hundred million years of skin feeding? Extended parental care in a Neotropical caecilian (Amphibia: Gymnophiona) |journal=Biology Letters |volume=4 |issue=4 |pages=358–361 |doi=10.1098/rsbl.2008.0217 |pmc=2610157 |pmid=18547909 }}</ref><ref>{{Cite journal |last1=Wilkinson |first1=Mark |last2=Sherratt |first2=Emma |last3=Starace |first3=Fausto |last4=Gower |first4=David J. |date=6 March 2013 |title=A New Species of Skin-Feeding Caecilian and the First Report of Reproductive Mode in Microcaecilia (Amphibia: Gymnophiona: Siphonopidae) |journal=PLOS ONE |language=en |volume=8 |issue=3 |article-number=e57756 |doi=10.1371/journal.pone.0057756 |issn=1932-6203 |pmc=3590283 |pmid=23483926 |bibcode=2013PLoSO...857756W |doi-access=free }}</ref>

''Herpele squalostoma'' caecilians vertically transmit the mother's microbiome to their offspring through maternal dermatophagy. In comparison to other amphibians, the extended parenting of caecilians can provide beneficial bacteria and fungi, but this transmission risks the spread of diseases like chytridiomycosis.<ref>{{Cite news |last=Quaglia |first=Sofia |date=18 October 2023 |title=These Amphibians Have a Taste for Their Mom's Skin |work=The New York Times |url=https://www.nytimes.com/2023/10/17/science/amphibians-microbiome-caecilians.html |access-date=22 October 2023 |archive-date=7 March 2024 |archive-url=https://web.archive.org/web/20240307233321/https://www.nytimes.com/2023/10/17/science/amphibians-microbiome-caecilians.html |url-status=live }}</ref><ref>{{Cite journal |last1=Kouete |first1=Marcel T. |last2=Bletz |first2=Molly C. |last3=LaBumbard |first3=Brandon C. |last4=Woodhams |first4=Douglas C. |last5=Blackburn |first5=David C. |date=15 May 2023 |title=Parental Care Contributes to Vertical Transmission of Microbes in a Skin-Feeding and Direct-Developing Caecilian |journal=Animal Microbiome |publisher=BioMed Central |volume=5 |issue=28 |page=28 |doi=10.1186/s42523-023-00243-x |doi-access=free |pmid=37189209 |pmc=10184399 }}</ref>

=== Diet === Caecilians are considered as generalist predators.<ref name="jstor.org">{{cite journal |last1=Govindappa |first1=Venu |title=An unusual diet of Ichthyophis caecilians |journal=Current Science |date=10 September 2016 |volume=111 |issue=111 |pages=793–795 |jstor=24908573 }}</ref> While caecilians are generally carnivorous, their diet differs between taxa. The stomach contents of wild caecilians include primarily soil ecosystem engineers<ref name="jstor.org"/> like earthworms, termites, lizards, moth larvae, and shrimp. Some species of caecilians will opportunistically consume newborn rodents, salmon eggs, and veal in laboratory conditions, as well as vertebrates such as scolecophidian snakes, lizards, small fish, and frogs.<ref>{{cite journal |last1=Govindappa |first1=Venu |title=An unusual diet of Ichthyophis caecilians |journal=Current Science |date=10 September 2016 |volume=111 |pages=793–795 |jstor=24908573 }}</ref><ref>{{Cite book |last=Schwenk |first=Kurt |title=Feeding: Form, Function, and Evolution in Tetrapod Vertebrates |publisher=Elsevier |year=2000 |isbn=978-0-08-053163-2 |pages=149–167 }}</ref>

== Cultural significance == As caecilians are a reclusive group, they are featured in only a few human myths and are considered repulsive by many cultures.

In the folklore of certain regions of India, caecilians are feared and reviled, based on the belief, mostly incorrect, that they are fatally venomous. While some species of caecillians have venomous bites, they are not thought to be fatal to adult humans. Caecilians in the Eastern Himalayas are colloquially known as "back ache snakes",<ref name=":2">Sathyabhamu, Das Biju, Rachunliu G Kamei, David Gower, & Mark Wilkinson (2009) "[https://www.cepf.net/sites/default/files/final_uofdelhi_caecilians_eastern_himalayas.pdf Conservation of Caecilians in the Eastern Himalayas Region] {{Webarchive|url=https://web.archive.org/web/20230516183354/https://www.cepf.net/sites/default/files/final_uofdelhi_caecilians_eastern_himalayas.pdf |date=16 May 2023 }}" ''Critical Ecosystem Partnership Fund Project Report''. pp. 1–22.</ref> while in the Western Ghats, ''Ichthyophis tricolor'' is considered to be more toxic than a king cobra.<ref name=":3">K. Ramachandran & Oommen V. Oommen (August 2008) "[https://www.academia.edu/12445871 Deep-rooted myths and their impact on the population of gymnophionan amphibians among the inhabited areas of Kerala, India] {{Webarchive|url=https://web.archive.org/web/20230516183354/https://www.academia.edu/12445871 |date=16 May 2023 }}" FrogLog v. 88. pp 3–5.</ref><ref name=":4">{{Cite book |last=Crump |first=Marty |title=Eye of Newt and Toe of Frog, Adder's Fork and Lizard's Leg |date=2015 |publisher=University of Chicago Press |doi=10.7208/chicago/9780226116143.001.0001 |isbn=978-0-226-11600-6 }}</ref> Despite deep cultural respect for the cobra and other dangerous animals, the caecilian is killed on sight by salt and kerosene.<ref name=":3" /> These myths have complicated conservation initiatives for Indian caecilians.<ref name=":3" /><ref name=":2" /><ref name=":4" />

''Crotaphatrema lamottei'', a rare species native to Mount Oku in Cameroon, is classified as a Kefa-ntie (burrowing creature) by the Oku. Kefa-ntie, a term also encompassing native moles and blind snakes, are considered poisonous, causing painful sores if encountered, contacted, or killed. According to Oku tradition, the ceremony to cleanse the affliction involves a potion composed of ground herbs, palm oil, snail shells, and chicken blood applied to and licked off of the left thumb.<ref>{{Cite journal |last1=Doherty-Bone |first1=Thomas M. |last2=Ndifon |first2=R.K. |last3=Gower |first3=David J. |date=2011 |title=Traditional indigenous perspectives on soil-dwelling vertebrates in Oku, Cameroon, with special reference to the caecilian ''Crotaphatrema lamottei'' |url=https://www.researchgate.net/publication/266736399 |journal=Herpetological Bulletin |volume=116 |pages=19–24 }}</ref>

South American caecilians have a variable relationship to local cultures.<ref name=":4" /> The minhocão, a legendary worm-like beast in Brazilian folklore, may be inspired by caecilians. Colombian folklore states that the aquatic caecilian, ''Typhlonectes natans'', can be manifested from a lock of hair sealed in a sunken bottle. In southern Mexico and Central America, ''Dermophis mexicanus'' is colloquially known as the "tapalcua", a name referencing the belief that it emerges to embed itself in the rear end of any unsuspecting person who chooses to relieve themself over its home. This may be inspired by their tendency to nest in refuse heaps.<ref name=":4" />

== See also == {{portal|Amphibians}} * Caecilians of the Western Ghats

== References == {{Reflist}}

== External links == * {{Commons category-inline|Gymnophiona}} * {{Wikispecies-inline|Gymnophiona}} {{Lissamphibia}} {{Amphibians}} {{Taxonbar|from1=Q28647812|from2=Q4758}} {{Authority control}}

Category:Caecilians Category:Gymnophiona Category:Mesozoic amphibians Category:Hettangian first appearances Category:Extant Early Jurassic first appearances Category:Taxa named by Johannes Peter Müller