View source for Sea snake

{{Use dmy dates|date=June 2023}}
{{Short description|Subfamily of reptiles}}
{{redirect|Sea snakes|other snake groups adapted to marine and brackish environments|List of marine snakes|the rock band|Sea Snakes}}{{For|sea snakes in mythology and cryptozoology|Sea serpent}}
{{Paraphyletic group
| auto = yes
| fossil_range = {{fossil range|23|0|[[Oligocene]] – Recent|ref=<ref>{{Cite journal |last1=Dudgeon |first1=Christine L. |last2=White |first2=William T. |date=2012 |title=First record of potential Batesian mimicry in an elasmobranch: juvenile zebra sharks mimic banded sea snakes? |url=http://www.publish.csiro.au/?paper=MF11211 |journal=Marine and Freshwater Research |language=en |volume=63 |issue=6 |pages=545 |doi=10.1071/MF11211 |issn=1323-1650}}</ref>}}
| image = Pelamis platura, Costa Rica.jpg
| image_caption = ''[[Yellow-bellied sea snake|Yellow-bellied sea snake (Hydrophis platurus)]]'' on a [[Costa Rica]] beach 
| parent = Elapidae
| includes = *[[Hydrophiinae]]
*[[Laticaudinae]]
| range_map = Sea Snake range.png
| range_map_caption = Range of sea snakes shown in lime green, except the widespread, pelagic [[yellow-bellied sea snake]]
}}

'''Sea snakes''', or '''coral reef snakes''', are [[Elapidae|elapid]] snakes that inhabit [[Marine (ocean)|marine]] environments for most or all of their lives. They belong to two subfamilies, [[Hydrophiinae]] and [[Sea krait|Laticaudinae]]. Hydrophiinae also includes Australasian terrestrial snakes, whereas Laticaudinae only includes the sea kraits (''Laticauda''), of which three species are found exclusively in freshwater. If these three freshwater species are excluded, there are 69 [[species]] of sea snakes divided among seven&nbsp;[[Genus|genera]].<ref name="ReptileDB">{{Cite web |editor-last=Uetz |editor-first=P. |editor-last2=Freed |editor-first2=P. |editor-last3=Aguilar |editor-first3=R. |editor-last4=Hošek |editor-first4=J.|year=2022 |title=Elapidae |url=http://reptile-database.reptarium.cz/advanced_search?taxon=Elapidae&submit=Search |access-date=2022-05-09 |website=The Reptile Database}}</ref>

Most sea snakes are [[venomous snake|venomous]], except the genus ''[[Emydocephalus]]'', which feeds almost exclusively on fish eggs.<ref>{{cite journal |journal=[[Toxicon]] |url=https://pubmed.ncbi.nlm.nih.gov/6658813/ |title=Lethal toxicity of venoms of snakes from the Coral Sea |first=S. A. |last=Minton |year=1983 |volume=21 |issue=6 |pages=901–902 |pmid= 6658813 |doi=10.1016/0041-0101(83)90082-x}}</ref> Sea snakes are extensively adapted to a fully aquatic life and are unable to move on land, except for the sea kraits, which have limited land movement. They are found in warm coastal waters from the [[Indian Ocean]] to the [[Pacific]] and are closely related to venomous terrestrial snakes in Australia.<ref name="Hutchings 2008 ">{{cite book |title=The Great Barrier Reef: Biology, Environment and Management |last= Hutchings|first= Pat |year=2008 |publisher=Csiro Publishing |isbn=9780643099975 |quote=Sea snakes are true reptiles closely related to Australian venomous terrestrial snakes. Indeed, both groups are included in a single subfamily, Hydrophiinae, by most modern herpetologists. |page=345 }}</ref>

All sea snakes have paddle-like tails and many have laterally compressed bodies that give them an [[eel]]-like appearance. Unlike fish, they do not have [[gill]]s and must surface regularly to breathe. Along with [[cetacea|Cetaceans]], they are among the most completely aquatic of all extant air-breathing [[vertebrate]]s.<ref name="P&G77">Parker HW, Grandison AGC. 1977. Snakes &ndash; a natural history. Second Edition. British Museum (Natural History) and Cornell University Press. 108 pp. 16 plates. LCCCN 76-54625. {{ISBN|0-8014-1095-9}} (cloth), {{ISBN|0-8014-9164-9}} (paper).</ref> Among this group are species with some of the most potent venoms of all [[snake]]s. Some have gentle dispositions and bite only when provoked, while others are much more aggressive.

==Description==
The majority of adult sea snakes species grow to between {{convert|120|and|150|cm|ft|0|abbr=on}} in length,<ref name="Sti74">Stidworthy J. 1974. Snakes of the World. Grosset & Dunlap Inc. 160 pp. {{ISBN|0-448-11856-4}}.</ref> with the largest, ''[[Hydrophis spiralis]]'', reaching a maximum of {{convert|3|m|ft|0|abbr=on}}.<ref name="Fic82">Fichter GS. 1982. Poisonous Snakes. A First Book. Franklin Watts. 66 pp. {{ISBN|0-531-04349-5}}.</ref> Their eyes are relatively small with a round pupil<ref name="Dit33">Ditmars RL. 1933. Reptiles of the World. Revised Edition. The MacMillan Company. 329 pp. 89 plates.</ref> and most have nostrils located dorsally.<ref name="Meh87">Mehrtens JM. 1987. Living Snakes of the World in Color. New York: Sterling Publishers. 480 pp. {{ISBN|0-8069-6460-X}}.</ref> The skulls do not differ significantly from those of terrestrial elapids, although their dentition is relatively primitive with short fangs and (with the exception of ''[[Emydocephalus]]'') as many as 18 smaller teeth behind them on the maxilla.<ref name="P&G77"/>

[[File:Laticauda colubrina (Wakatobi).jpg|thumb|left|upright|Yellow-lipped sea krait, ''[[Laticauda colubrina]]'']]
Most sea snakes are completely aquatic and have adapted to sea environments in many ways, the most characteristic of which is a paddle-like tail that has improved their swimming ability.<ref name="RAS-FAO">{{cite book |title=The living marine resources of the Western Central Pacific |editor=Kent E. Carpenter |editor2=Volker H. Niem |chapter=Sea snakes |author=Rasmussen, A.R. |year=2001 |pages=3987–4008 |series=FAO species identification guide for fishery purposes |url=http://www.fao.org/docrep/009/w7191e/w7191e00.htm |chapter-url=http://www.fao.org/tempref/docrep/fao/009/y0870e/y0870e65.pdf |publisher=Food and Agriculture Organization of the United Nations |location=Rome |access-date=7 August 2007 |archive-date=6 February 2019 |archive-url=https://web.archive.org/web/20190206034713/http://www.fao.org/docrep/009/w7191e/w7191e00.HTM |url-status=dead }}</ref> To a varying degree, the bodies of many species are laterally compressed, especially in the [[pelagic]] species. This has often caused the [[ventral scales]] to become reduced in size, even difficult to distinguish from the adjoining scales. Their lack of ventral scales means they have become virtually helpless on land, but as they live out their entire lifecycles at sea, they have no need to leave the water.<ref name="Sti74"/><ref name="Meh87"/>

The only [[genus]] that has retained the enlarged ventral scales is the sea kraits, ''[[Laticauda]]'', with only five species. These snakes are considered to be more primitive, as they still spend much of their time on land, where their ventral scales afford them the necessary grip.<ref name="Sti74"/><ref name="Meh87"/> ''Laticauda'' species are also the only sea snakes with [[internasal scales]]; that is, their nostrils are not located dorsally.<ref name="RAS-FAO"/>

Since a snake's tongue can fulfill its [[Sense of smell|olfactory function]] more easily under water, its action is short compared to that of terrestrial snake species. Only the forked tips protrude from the mouth through a divided notch in the middle of the [[rostral scale]].<ref name="P&G77"/> The nostrils have valves consisting of a specialized spongy tissue to exclude water, and the windpipe can be drawn up to where the short nasal passage opens into the roof of the mouth. This is an important adaptation for an animal that must surface to breathe, but may have its head partially submerged when doing so. The lung has become very large and extends almost the entire length of the body, although the rear portion is thought to have developed to aid buoyancy rather than to exchange gases. The extended lung possibly also serves to store air for dives.<ref name="Sti74"/><ref name="Meh87"/>

Most species of sea snakes are able to [[cutaneous respiration|respire through the top of their skin]]. This is unusual for reptiles, because their skin is thick and scaly, but experiments with the black-and-yellow sea snake, ''[[Hydrophis platurus]]'' (a [[pelagic]] species), have shown this species can satisfy about 25% of its oxygen requirements in this manner, which allows for prolonged dives.<ref name="C&L04">Campbell JA, Lamar WW. 2004. The Venomous Reptiles of the Western Hemisphere. Comstock Publishing Associates, Ithaca and London. 870 pp. 1500 plates. {{ISBN|0-8014-4141-2}}.</ref>

[[File:Laticauda laticaudata.jpg|thumb|right|260px|Blue-lipped sea krait, ''[[Laticauda laticaudata]]'']]
Like other land animals that have adapted to life in a marine environment, sea snakes ingest considerably more salt than their terrestrial relatives through their diets, when seawater is inadvertently swallowed. Because of this, a more effective means of regulating the salt concentration of their blood is required. In sea snakes, the posterior sublingual glands, located under and around the tongue sheath, allow them to expel salt with their tongue action.<ref name="P&G77"/><ref name="Meh87"/>

Scalation among sea snakes is highly variable. As opposed to terrestrial snake species that have imbricate scales to protect against abrasion, the scales of most pelagic sea snakes do not overlap. Reef-dwelling species, such as ''[[Aipysurus]]'', do have imbricate scales to protect against the sharp coral. The scales themselves may be smooth, [[keeled scales|keeled]], spiny, or granular, the latter often looking like warts. ''Pelamis'' has body scales that are "peg-like", while those on its tail are juxtaposed hexagonal plates.<ref name="Meh87"/>

== Sensory abilities ==
[[Visual perception|Vision]], [[Chemoreceptor|chemoreception]] (tongue-flicking), and [[hearing]] are important senses for terrestrial snakes, but these [[stimulus (physiology)|stimuli]] become distorted in water.<ref>{{Cite journal|last1=Shine|first1=R.|last2=Phillips|first2=B.|last3=Waye|first3=H.|last4=LeMaster|first4=M.|last5=Mason|first5=R. T.|date=2003-05-14|title=Chemosensory cues allow courting male garter snakes to assess body length and body condition of potential mates|journal=Behavioral Ecology and Sociobiology|language=en|volume=54|issue=2|pages=162–166|doi=10.1007/s00265-003-0620-5|s2cid=22852516|issn=0340-5443}}</ref><ref>{{Cite journal|last=Young|first=Bruce A.|date=2003-09-01|title=Snake bioacoustics: toward a richer understanding of the behavioral ecology of snakes|journal=The Quarterly Review of Biology|volume=78|issue=3|pages=303–325|issn=0033-5770|pmid=14528622|doi=10.1086/377052|s2cid=22195556}}</ref> The poor visibility, chemical dilution, and limitation of ground-borne vibrations under water suggest that sea snakes and sea kraits may have unique sensory abilities to compensate for the relative lack of other sensory cues.<ref name=":0">{{Cite book|title=Sensory Evolution on the Threshold: Adaptations in Secondarily Aquatic Vertebrates|date=2008-02-04|publisher=University of California Press|isbn=9780520252783|edition=1|language=en}}</ref>

Relatively little is known about sea snake vision. A study of [[Photoreceptor cell|photoreceptors]] in the [[retina]] of spine-bellied, ''[[Lapemis curtus]],'' and horned, ''[[Acalyptophis peronii]]'', sea snakes found three classes of [[opsin]]s all from [[cone cell]]s.<ref>{{Cite journal|last1=Hart|first1=Nathan S.|last2=Coimbra|first2=João Paulo|last3=Collin|first3=Shaun P.|last4=Westhoff|first4=Guido|date=2012-04-15|title=Photoreceptor types, visual pigments, and topographic specializations in the retinas of hydrophiid sea snakes|journal=The Journal of Comparative Neurology|volume=520|issue=6|pages=1246–1261|doi=10.1002/cne.22784|issn=1096-9861|pmid=22020556|s2cid=8011090}}</ref> Despite the absence of [[rod cell]]s in sea snake eyes, Simeos ''et al.'' found the [[rhodopsin]] (''rh1''), the opsin of the rods, still [[Expressed gene|expressed]]<ref>{{Cite journal|last1=Simões|first1=Bruno F.|last2=Sampaio|first2=Filipa L.|last3=Loew|first3=Ellis R.|last4=Sanders|first4=Kate L.|last5=Fisher|first5=Robert N.|last6=Hart|first6=Nathan S.|last7=Hunt|first7=David M.|last8=Partridge|first8=Julian C.|last9=Gower|first9=David J.|date=2016-01-27|title=Multiple rod–cone and cone–rod photoreceptor transmutations in snakes: evidence from visual opsin gene expression|journal=Proc. R. Soc. B|language=en|volume=283|issue=1823|pages=20152624|doi=10.1098/rspb.2015.2624|issn=0962-8452|pmc=4795032|pmid=26817768}}</ref> suggesting that in sea snakes some cones may be transmuted rods. Behavioural observations indicate that vision has a limited role for catching prey and mate selection, but sound [[vibration]]s and chemoreception may be important.<ref>{{Cite book|url=http://www.environment.gov.au/system/files/pages/dc11235d-8b3b-43f7-b991-8429f477a1d4/files/36-fauna-2a-squamata-hydrophiidae.pdf|title=Fauna of Australia|author1=Heatwole, H  |author2=Cogger, H|publisher=AGPS|year=1993|location=Canberra, Australia|pages=16}}</ref><ref>{{Cite book|url=https://books.google.com/books?id=80ERtB6qgGgC|title=Sea Snakes|last=Heatwole|first=Harold|date=1999-01-01|publisher=UNSW Press|isbn=9780868407760|language=en}}</ref> One study identified small sensory organs on the head of ''[[Lapemis curtus]]''<ref>{{Cite journal|url=https://www.researchgate.net/publication/233682064|title=Scale Sensillae of the File Snake (Serpentes: Acrochordidae) and Some Other Aquatic and Burrowing Snakes|journal=Netherlands Journal of Zoology|volume=47|issue=4|pages=443–456|doi=10.1163/156854297X00111|access-date=2016-04-02|year=1996|last1=Van Der Kooij|first1=Jeroen|last2=Povel|first2=David}}</ref> similar to the mechanoreceptors in [[alligator]]s and aquatic snake [[Acrochordidae|Acrochodus]] that are used to sense the movement of fish prey.<ref>{{Cite journal|last=Soares|first=Daphne|date=2002-05-16|title=Neurology: An ancient sensory organ in crocodilians|journal=Nature|language=en|volume=417|issue=6886|pages=241–242|doi=10.1038/417241a|issn=0028-0836|pmid=12015589|bibcode=2002Natur.417..241S |s2cid=1922782}}</ref> Westhoff ''et al.'' recorded [[Threshold potential|auditory brain responses]] to [[vibration]] underwater in ''Lapemis curtus'',<ref>{{Cite journal|last1=Westhoff|first1=Guido|last2=Fry|first2=Bryan G.|last3=Bleckmann|first3=Horst|date=2005-01-01|title=Sea snakes (''Lapemis curtus'') are sensitive to low-amplitude water motions|journal=Zoology |volume=108|issue=3|pages=195–200|doi=10.1016/j.zool.2005.07.001|issn=0944-2006|pmid=16351967}}</ref> which are sensitive enough to detect movement in prey, but were not as sensitive as [[Lateral line|fish lateral line]] systems. Similarly, vision appears to be of limited importance for finding mates. Shine experimented with applying skin secretions ([[pheromone]]s) to snake-like objects to see if male turtle-headed sea snakes, ''[[Emydocephalus annulatus]],'' are attracted to female pheromones. Shine found that although vision may be useful over short distances (less than {{convert|1|m|ft|0|abbr=on|disp=sqbr}}), pheromones are more important once the male comes in physical contact with an object.<ref>{{Cite journal|last=Shine|first=R.|date=2005-01-13|title=All at sea: aquatic life modifies mate-recognition modalities in sea snakes (''Emydocephalus annulatus'', Hydrophiidae)|journal=Behavioral Ecology and Sociobiology|language=en|volume=57|issue=6|pages=591–598|doi=10.1007/s00265-004-0897-z|s2cid=34698605|issn=0340-5443}}</ref>

The olive sea snake, ''[[Aipysurus laevis]]'', has been found to have photoreceptors in the skin of its tail, allowing it to detect light and presumably ensuring it is completely hidden, including its tail, inside coral holes during the day. While other species have not been tested, ''A.&nbsp;laevis'' possibly is not unique among sea snakes in this respect.<ref name="Z&H90">{{cite journal | last1 = Zimmerman | first1 = K | last2 = Heatwole | first2 = H | year = 1990 | title = Cutaneous Photoreception: A New Sensory Mechanism for Reptiles | journal = Copeia | volume = 1990 | issue = 3| pages = 860–862 | doi=10.2307/1446454| jstor = 1446454 }}</ref>

Other unique senses, such as [[Magnetoreception|electromagnetic reception]] and [[Hearing|pressure]] detection,<ref>{{Cite journal|last1=Liu|first1=Y.-L.|last2=Lillywhite|first2=H. B.|last3=Tu|first3=M.-C.|date=2010-07-03|title=Sea snakes anticipate tropical cyclone|journal=Marine Biology|language=en|volume=157|issue=11|pages=2369–2373|doi=10.1007/s00227-010-1501-x|s2cid=85297798|issn=0025-3162}}</ref> have been proposed for sea snakes, but scientific studies have yet to be performed to test these senses.<ref name=":0" />

==Distribution and habitat==
Sea snakes are mostly confined to the warm [[Tropics|tropical]] waters of the [[Indian Ocean]] and the western [[Pacific Ocean]],<ref name="Sti74"/> with a few species found well out into [[Oceania]].<ref name="USN91">U.S. Navy. 1991. Poisonous Snakes of the World. US Govt. New York: Dover Publications Inc. 203 pp. {{ISBN|0-486-26629-X}}.</ref>  The geographic range of one species, ''[[Pelamis platurus]]'', is wider than that of any other reptile species, except for a few species of sea turtles.<ref name="P&G77"/> It extends from the east coast of [[Africa]], from [[Djibouti]] in the north to [[Cape Town]] in the south,<ref name="SB95">Spawls S, Branch B. 1995. The Dangerous Snakes of Africa. Ralph Curtis Books. Dubai: Oriental Press. 192 pp. {{ISBN|0-88359-029-8}}.</ref> across the Indian Ocean, the Pacific, south as far as the northern coast of [[New Zealand]],<ref name="USN91"/><ref>{{cite journal |vauthors=Slaughter RJ, Beasley DM, Lambie BS, Schep LJ |title=New Zealand's venomous creatures |journal=New Zealand Medical Journal |volume=122 |issue=1290 |pages=83–97 |year=2009 |pmid=19319171}}</ref> all the way to the western coast of the [[Americas]], where it occurs from northern [[Peru]] in the south (including the [[Galápagos Islands]]) to the [[Gulf of California]] in the north. Isolated specimens have been found as far north as [[San Diego, California|San Diego]] and [[Oxnard, California|Oxnard]] in the [[United States]].<ref>{{Cite web|url=https://www.nbcsandiego.com/news/local/venomous-yellow-bellied-sea-snake-washes-up-on-coronado-beach/116321/|title=Venomous Yellow-Bellied Sea Snake Washes Up on Coronado Beach}}</ref>

Sea snakes do not occur in the [[Atlantic Ocean]].<ref name="Meh87"/>  ''Pelamis'' possibly would be found there were it not for the cold currents off [[Namibia]] and western [[South Africa]] that keep it from crossing into the eastern South Atlantic, or south of 5°S latitude along the South American west coast. Sea snakes do not occur in the [[Red Sea]], believed to be due to its increased salinity, so no danger exists of them crossing through the [[Suez Canal]]. A lack of salinity is also thought to be the reason why ''Pelamis'' has not crossed into the [[Caribbean]] via the [[Panama Canal]].<ref name="P&G77"/>

Despite their marine adaptations, most sea snakes prefer shallow waters near land, around islands, and especially somewhat sheltered waters, as well as near estuaries.<ref name="Sti74"/><ref name="RAS-FAO"/> They may swim up rivers and have been reported as far as {{convert|160|km|-1|abbr=on}} from the sea.<ref name="RAS-FAO"/> Others, such as ''P. platurus'', are [[pelagic]] and are found in drift lines, slicks of floating debris brought together by surface currents.<ref name="NS90">[https://www.newscientist.com/article/mg12817424.200-the-sea-snakes-are-comingc-will-global-warming-bring-theworlds-most-poisonous-snakes-to-britains-shores-zoologists-have-justbegun-to-understand-how-they-survive-in-the-open-sea-.html The sea snakes are coming] at [https://www.newscientist.com/ NewScientist]. Accessed 13 January 2009.</ref> Some sea snakes inhabit mangrove swamps and similar brackishwater habitats, and two landlocked freshwater forms are found: ''[[Hydrophis semperi]]'' occurs in [[Taal Lake|Lake Taal]] in the [[Philippines]], and ''[[Laticauda crockeri]]'' in Lake Te Nggano on [[Rennell Island]] in the [[Solomon Islands]].<ref name="Meh87"/>

==Behavior==
Sea snakes are generally reluctant to bite,<ref name="Sti74"/><ref name="Fic82"/> and are usually considered to be mild-tempered, although variation is seen among species and individuals.<ref name="USN91"/> Some species, such as ''P. platurus'', which feed by simply gulping down their prey, are more likely to bite when provoked because they seem to use their venom more for defense. Others, such as ''Laticauda'' spp., use their venom for prey immobilization. Sea snakes are often handled without concern by local fishermen who unravel and toss them back into the water barehanded, usually without getting bitten, when the snakes frequently become entangled in fishing nets.<ref name="Sti74"/><ref name="Meh87"/> Species reported as much more aggressive include ''[[Aipysurus laevis]]'', ''[[Astrotia stokesii]]'', ''[[Enhydrina schistosa]]'', ''[[Enhydrina zweifeli]]'', and ''[[Hydrophis ornatus]]''.<ref name="RAS-FAO"/>

[[File:Aipysurus laevis.jpg|thumb|Olive sea snake, ''[[Aipysurus laevis]]'']]
On land, their movements become very erratic. They crawl awkwardly in these situations and can become quite aggressive, striking wildly at anything that moves, although they are unable to coil and strike in the manner of terrestrial snakes.<ref name="Fic82"/><ref name="Dit33"/>

Sea snakes appear to be active both day and night. In the morning, and sometimes late in the afternoon, they can be seen at the surface basking in the sunlight, and they dive when disturbed.<ref name="Sti74"/> They have been reported swimming at depths over {{convert|90|m|ft|-1|abbr=on}}, and can remain submerged for as long as a few hours, possibly depending on temperature and degree of activity.<ref name="Fic82"/><ref name="USN91"/>

Sea snakes have been sighted in huge numbers. For example, in 1932, a steamer in the [[Strait of Malacca]], off the coast of [[Malaysia]], reported sighting "millions" of ''[[Astrotia stokesii]]'', a relative of ''Pelamis''; these reportedly formed a line of snakes {{convert|3|m|ft|0|abbr=on}} wide and {{convert|100|km|mi|-1|abbr=on}} long.<ref name="NS90"/> The cause of this phenomenon is unknown, although it likely has to do with reproduction.<ref name="P&G77"/> They can sometimes be seen swimming in schools of several hundred, and many dead specimens have been found on beaches after typhoons.<ref name="Dit33"/>

==Ecology==
They feed on small fish and occasionally young octopus. They are often associated with the [[Platylepas ophiophila|sea snake barnacle]] (''Platylepas ophiophila''), which attaches to their skin.<ref name=Vernberg>{{cite book|author=Vernberg, F. John |title=Behavior and Ecology|url=https://books.google.com/books?id=Re_sBe-xQtQC&pg=PA189 |year=2014 |publisher=Elsevier Science |isbn=978-0-323-16269-2 |page=186}}</ref>

==Reproduction==
Except for a single genus, all sea snakes are [[ovoviviparous]]; the young are born alive in the water where they live their entire lives.<ref name="Meh87"/> In some species, the young are quite large, up to half as long as the mother.<ref name="Fic82"/> The one exception is the genus ''Laticauda'', which is [[oviparous]]; its five species all lay their eggs on land.<ref name="Meh87"/>

==Venom==
Like their relatives in the family Elapidae, the majority of sea snakes are highly venomous. They rarely inject their venom when biting, so venomous bites to humans are rare.<ref name="RAS-FAO"/> For example, ''[[Yellow-bellied sea snake|Hydrophis platurus]]'' has a venom more potent than any terrestrial snake species in [[Costa Rica]] based on [[LD50|LD<sub>50</sub>]], but despite its abundance in the waters off its western coast, few human fatalities have been reported.<ref name="C&L04"/> The death of a trawler fisherman in Australian waters during 2018 was reported to be the region's first sea snake fatality since a pearl diver was killed in 1935.<ref name="Smith2018">{{cite news |last1=Smith |first1=Emily |title=Fisherman's deadly encounter with sea snake incredibly rare |url=https://www.abc.net.au/news/2018-10-08/sea-snake-death-trawler-harry-evans-english/10351010 |work=ABC News |date=8 October 2018 |language=en-AU}}</ref>

Bites in which envenomation does occur are usually painless and may not even be noticed when contact is made. Teeth may remain in the wound. Usually, little or no swelling occurs, and rarely are any nearby [[lymph node]]s affected. The most important symptoms are [[rhabdomyolysis]] (rapid breakdown of skeletal muscle tissue) and paralysis. Early symptoms include headache, a thick-feeling tongue, thirst, sweating, and vomiting. The venom is very slow acting and symptoms that happen from little as 30&nbsp;minutes to several hours after the bite include generalized aching, stiffness, and tenderness of muscles all over the body. Passive stretching of the muscles is also painful, and [[trismus]], which is similar to [[tetanus]], is common. This is followed later on by symptoms typical of other [[Elapidae|elapid]] envenomations, a progressive flaccid paralysis, starting with [[Ptosis (eyelid)|ptosis]] and paralysis of voluntary muscles. Paralysis of muscles involved in swallowing and respiration can be fatal.<ref name="War-C&L04">Warrell DA. 2004. Snakebites in Central and South America: Epidemiology, Clinical Features, and Clinical Management. ''In'' Campbell JA, Lamar WW. 2004. The Venomous Reptiles of the Western Hemisphere. Comstock Publishing Associates, Ithaca and London. 870 pp. 1500 plates. {{ISBN|0-8014-4141-2}}.</ref>

Vick ''et al'' (1975) estimated that the LD<sub>50</sub> of three sea snake venoms (''H. platurus'', ''L. semifasciata'' and ''L. laticaudata'') for a 70 kg human range from 7.7 to 21 mg. Data from the only sea snake venom conducted in monkeys at that time suggested that primates were slightly more resistant to the venom effects on a dose response basis than mice. Ishikawa ''et al'' (1985) indicated a substantially lower binding affinity between sea snake neurotoxin and human and chimpanzee [[Nicotinic acetylcholine receptor|AChR's]] compared to that in other animals. In humans, the venom targets appear mainly to be the cell walls of voluntary (skeletal) muscles and distal tubular portions of the kidney including the [[loop of Henle]], the second convoluted tubule and the collecting tubules. Sitprija ''et al'' (1973) found evidence of [[tubular necrosis]] throughout all portions of the renal tubules in two patients severely envenomated by sea snakes. Sea snake venoms in humans are thus more often myotoxic and/or nephrotoxic rather than neurotoxic.<ref>{{Cite book |last=Gopalakrishnakone |first=P. |url=https://books.google.com/books?id=i2yTrfdnnq8C&dq=LD50+monkey+sea+snake&pg=PA140 |title=Sea Snake Toxinology |date=1994 |publisher=NUS Press |isbn=978-9971-69-193-6 |language=en}}</ref>

==Taxonomy==
{{cladogram|title=Cladogram
|caption=Cladogram showing the basic evolutionary relationships among sea snakes, sea kraits and other venomous terrestrial snakes. Sea kraits diverged earlier from the rest of Australasian elapids, in contrast other sea snakes are more closely related to Australasian elapids then they are to sea kraits.
|clades={{clade| style=font-size:85%;line-height:75%;
|label1=[[Elapidae]]
|1={{clade 
	|1=[[Cobra]]
	|label2=Hydrophiinae
	|2={{clade
		|label1='''sea kraits'''
		|1=''Laticauda''
		|2={{clade
			|1=''[[Notechis]]''
			|label2='''other sea snakes'''
			|2={{clade
				|1={{clade
					|1=''Emydocephalus''
					|2=''Aipysurus''
					}}
				|2={{clade
					|1=''Hydrelaps''
					|2=''Hydrophis''
					}}
				}}
			}}
		}}
	}}
}}
}}
Sea snakes were at first regarded as a unified and separate family, the Hydrophiidae, that later came to comprise two subfamilies: the Hydrophiinae, or true/aquatic sea snakes (now 6&nbsp;genera with 64&nbsp;species), and the more primitive Laticaudinae, or sea kraits (one genus, ''Laticauda'', with eight species). Eventually, as just how closely related the sea snakes are to the elapids became clear, the taxonomic situation became less well-defined. Some taxonomists responded by moving the sea snakes to the Elapidae. Most taxonomists now place the sea snakes in the elapid subfamilies Hydrophiinae and Laticaudinae, although the latter may be omitted if ''Laticauda'' is included in the Hydrophiinae. Unlike the traditional Hydrophiinae, the Hydrophiinae as currently seen also includes Australasian terrestrial elapids.<ref name="ITIS"/><ref name="ReptileDB"/><ref name="Dit33"/><ref name="Meh87"/><ref name="Hutchings 2008 "/>
{{-}}
{| class="wikitable"
! Genus<ref name="ReptileDB"/>
! Taxon authority<ref name="ITIS">{{ITIS |id=174348 |taxon=Elapidae |access-date=7 August 2007}}</ref>
! Species<ref name="ReptileDB"/>
! {{nowrap|Subsp.<ref name="ITIS"/>{{efn |name=subspecies|Not counting the nominate subspecies}}}}
! Common name<ref name="NRDB">[http://www.jcvi.org/reptiles/families/elapidae.php Elapidae] {{Webarchive|url=https://web.archive.org/web/20081011004551/http://www.jcvi.org/reptiles/families/elapidae.php |date=2008-10-11 }} at the [http://reptile-database.org/ New Reptile Database]. Accessed 12 August 2007.</ref>
! Geographic range<ref name="NRDB"/>
|-
|''[[Aipysurus]]''
|[[Bernard Germain Étienne comte de La Ville-sur-Illon La Cépède|Lacépède]], 1804
|align="center"|9
|align="center"|1
|olive sea snakes
|[[Timor Sea]], South China Sea, Gulf of Thailand, and coasts of Australia (Northern Territory, Queensland, Western Australia), New Caledonia, [[Loyalty Islands]], southern [[New Guinea]], [[Indonesia]], western [[Malaysia]] and [[Vietnam]]
|-
|''[[Emydocephalus]]''
|[[Gerard Krefft|Krefft]], 1869
|align="center"|3
|align="center"|0
|turtlehead sea snakes
|the coasts of Timor (Indonesian Sea), [[New Caledonia]], Australia (Northern Territory, Queensland, Western Australia), and in the [[Southeast Asia]]n sea along the coasts of [[China]], [[Taiwan]], [[Japan]], and the Ryukyu Islands
|-
|''[[Ephalophis]]''
|[[Malcolm Arthur Smith|M.A. Smith]], 1931
|align="center"|1
|align="center"|0
|Grey's mudsnake
|northwestern [[Australia]]
|-
|''[[Hydrelaps]]''
|[[George Albert Boulenger|Boulenger]], 1896
|align="center"|1
|align="center"|0
|Port Darwin mudsnake
|northern Australia, southern New Guinea
|-
|''[[Hydrophis]]''
|[[Pierre André Latreille|Latreille]] ''in'' [[Charles-Nicolas-Sigisbert Sonnini de Manoncourt|Sonnini]] & [[Pierre André Latreille|Latreille]], 1801
|align="center"|49
|align="center"|3
|sea snakes
|[[Malay Archipelago|Indo-Australian]] and [[Southeast Asia]]n waters.<ref name="Cyb">[http://www.cyberlizard.plus.com/venomous5.htm The Hydrophiidae] at [http://www.cyberlizard.plus.com/ Cyberlizard's home pages]. Accessed 12 August 2007.</ref>
|-
|''[[Laticauda]]''
|[[Josephus Nicolaus Laurenti|Laurenti]], 1768
|align="center"|8
|align="center"|0
|sea kraits
|Southeast Asian and Indo-Australian waters
|-
|''[[Parahydrophis]]''
|Burger & Natsuno, 1974
|align="center"|1
|align="center"|0
|northern mangrove sea snake
|northern Australia, southern New Guinea
|}

{{notelist}}

===Molecular studies===

Molecular data studies suggest all three monotypic semiaquatic genera (''[[Ephalophis]]'', ''[[Parahydrophis]]'' and ''[[Hydrelaps]]'') are early diverging lineages.<ref name=Sanders2012>{{cite journal | last1 = Sanders | first1 = KL |author-link=Kate Sanders | last2 = Lee | first2 = MS | last3 = Mumpuni | first3 = Bertozzi T | last4 = Rasmussen | first4 = AR | year = 2012 | title = Multilocus phylogeny and recent rapid radiation of the viviparous sea snakes (Elapidae: Hydrophiinae) | journal = Molecular Phylogenetics and Evolution | volume = 66| issue = 3| pages = 575–591| doi = 10.1016/j.ympev.2012.09.021 | pmid=23026811}}</ref>

==Captivity==
[[File:Hydrophis cyanocinctus lores.jpg|thumb|240px|''[[Hydrophis cyanocinctus]]'']]
At best, sea snakes make difficult captives. Ditmars (1933) described them as nervous and delicate captives that usually refuse to eat, preferring only to hide in the darkest corner of the tank.<ref name="Dit33"/> Over 50&nbsp;years later, Mehrtens wrote in 1987 that although they were rarely displayed in Western zoological parks, some species were regularly on display in Japanese aquariums. The available food supply limits the number of species that can be kept in captivity, since some have diets that are too specialized. Also, some species appear intolerant of handling, or even being removed from the water.  Regarding their requirements in captivity, the ''[[Laticauda]]'' species need to be able to exit the water somewhere at about {{convert|29|°C|abbr=on}}, along with a submerged shelter. Species that have done relatively well in captivity include the ringed sea snake, ''[[Hydrophis cyanocinctus]]'', which feeds on [[fish]] and [[eel]]s in particular. ''[[Pelamis platurus]]'' has done especially well in captivity, accepting small fish, including [[goldfish]]. Housing them in round tanks, or in rectangular tanks with well-rounded corners, prevents snakes from damaging their snouts on the sides.<ref name="Meh87"/>

==Conservation status==
Most sea snakes are not on the [[CITES]] protection lists.<ref name="RAS-FAO"/><ref name="CITES">[http://www.unep-wcmc.org/isdb/CITES/Taxonomy/tax-order-result.cfm?source=animals&RequestTimeout=1200&displaylanguage=eng&Order=141 Serpentes] {{Webarchive|url=https://web.archive.org/web/20200530193932/https://www.speciesplus.net/ |date=2020-05-30 }} at [http://www.cites.org/ CITES]. Accessed 11 August 2007.</ref> One species, ''[[Laticauda crockeri]]'', is classified as vulnerable. Several species of ''[[Aipysurus]]'' are listed with conservation status of greater concern, the Timor species ''[[Aipysurus fuscus|A.&nbsp;fuscus]]'' is known to be endangered, and two others found in seas north of Australia, the leaf-scaled ''[[Aipysurus foliosquama|A.&nbsp;foliosquama]]'' and short-nosed ''[[Aipysurus apraefrontalis|A.&nbsp;apraefrontalis]]'', are classified as [[critically endangered]] according to the [[IUCN]] Red List of Threatened Species.<ref>{{cite web |title=Red list search |url=http://www.iucnredlist.org/apps/redlist/search |website=[[IUCN Red List]] |access-date=16 June 2023 |archive-url=https://web.archive.org/web/20091106014521/http://www.iucnredlist.org/apps/redlist/search |archive-date=November 6, 2009 |language=en}}</ref>

==See also==
* [[List of marine reptiles]]
* [[Snakebite]]
* [[Sea serpent]]

==References==
{{Reflist}}

==Further reading==
{{refbegin}}
* Graham JB, Lowell WR, Rubinoff I, Motta J. 1987. Surface and subsurface swimming of the sea snake ''Pelamis platurus''. J. exp. Biol. 127, 27-44. [http://jeb.biologists.org/cgi/reprint/127/1/27.pdf PDF] at the [Journal of Experimental Biology]. Accessed 7 August 2007.
* Rasmussen AR. 1997. Systematics of sea snakes; a critical review. Symp. Zool. Soc. London 70, 15-30.
* Smith MA. 1926. Monograph of the sea snakes (Hydrophiidae). British Museum of Natural History, London.
* Voris HK. 1977. A phylogeny of the sea snakes (Hydrophiidae). Fieldiana Zool. 70, 79-169.
* Whitaker R. 1978. Common Indian Snakes: A Field Guide. Macmillan India Limited.
{{refend}}

==External links==
*[http://www.mesa.edu.au/sea_snakes/sea_snakes01.asp Sea Snakes in Australia]
*[http://scuba-doc.com/underwater-predators-sea-snakes/ Sea Snakes] at [http://www.scuba-doc.com/ Scubadoc's Diving Medicine Online]. Accessed 6 August 2007.
*[https://divehappy.com/indonesia/diving-gunung-api-volcano-of-the-sea-snakes/ Diving Gunung Api: Volcano Of The Sea Snakes] - first hand account of scuba divers interacting with sea snakes at the Indonesian volcano Gunung Api, June 2009

{{good article}}

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[[Category:Sea snakes| ]]
[[Category:Taxa named by Malcolm Arthur Smith]]