Sea snake
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Sea snakes, or coral reef snakes, are
elapid Elapidae (, commonly known as elapids ; grc, ἔλλοψ ''éllops'' "sea-fish") is a family of snakes characterized by their permanently erect fangs at the front of the mouth. Most elapids are venomous, with the exception of the genus Emydoce ...
snakes that inhabit marine environments for most or all of their lives. They belong to two subfamilies,
Hydrophiinae Hydrophiinae is a subfamily of venomous snakes in the family Elapidae. It contains most sea snakes and many genera of venomous land snakes found in Australasia, such as the taipans (''Oxyuranus''), tiger snakes (''Notechis''), brown snakes (' ...
and
Laticaudinae Sea kraits are a genus of venomous elapid sea snakes (subfamily: Laticaudinae), ''Laticauda''. They are semiaquatic, and retain the wide ventral scales typical of terrestrial snakes for moving on land, but also have paddle-shaped tails for swimmi ...
. 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 In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
of sea snakes divided between seven 
genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...
. Most sea snakes are
venomous Venom or zootoxin is a type of toxin produced by an animal that is actively delivered through a wound by means of a bite, sting, or similar action. The toxin is delivered through a specially evolved ''venom apparatus'', such as fangs or a sti ...
, except the genus ''
Emydocephalus ''Emydocephalus'' is a genus of sea snakes, also known as turtle-headed sea snakes, in the family Elapidae. Unlike most sea snakes, all species of ''Emydocephalus'', have an absence of teeth on their dentary and palatine bones, and lack venom, m ...
'', which feeds almost exclusively on fish eggs. 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 The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by th ...
to the
Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...
and are closely related to venomous terrestrial snakes in Australia. All sea snakes have paddle-like tails and many have laterally compressed bodies that give them an
eel Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 19 families, 111 genera, and about 800 species. Eels undergo considerable development from the early larval stage to the eventual adult stage ...
-like appearance. Unlike fish, they do not have
gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...
s and must surface regularly to breathe. Along with
whales Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and ...
, they are among the most completely aquatic of all extant air-breathing
vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
s.Parker HW, Grandison AGC. 1977. Snakes – a natural history. Second Edition. British Museum (Natural History) and Cornell University Press. 108 pp. 16 plates. LCCCN 76-54625. (cloth), (paper). Among this group are species with some of the most potent venoms of all
snake Snakes are elongated, Limbless vertebrate, limbless, carnivore, carnivorous reptiles of the suborder Serpentes . Like all other Squamata, squamates, snakes are ectothermic, amniote vertebrates covered in overlapping Scale (zoology), scales. Ma ...
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 in length,Stidworthy J. 1974. Snakes of the World. Grosset & Dunlap Inc. 160 pp. . with the largest, ''
Hydrophis spiralis ''Hydrophis spiralis'', commonly known as the yellow sea snake, is a species of venomous sea snake in the family Elapidae. Description This is perhaps the longest species of sea-snake, measuring up to ; however, most specimens do not exceed 2.0 ...
'', reaching a maximum of .Fichter GS. 1982. Poisonous Snakes. A First Book. Franklin Watts. 66 pp. . Their eyes are relatively small with a round pupilDitmars RL. 1933. Reptiles of the World. Revised Edition. The MacMillan Company. 329 pp. 89 plates. and most have nostrils located dorsally.Mehrtens JM. 1987. Living Snakes of the World in Color. New York: Sterling Publishers. 480 pp. . 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 ''Emydocephalus'' is a genus of sea snakes, also known as turtle-headed sea snakes, in the family Elapidae. Unlike most sea snakes, all species of ''Emydocephalus'', have an absence of teeth on their dentary and palatine bones, and lack venom, m ...
'') as many as 18 smaller teeth behind them on the maxilla. 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. To a varying degree, the bodies of many species are laterally compressed, especially in the
pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...
species. This has often caused the
ventral scales In snakes, the ventral scales or gastrosteges are the enlarged and transversely elongated scales that extend down the underside of the body from the neck to the anal scale. When counting them, the first is the anteriormost ventral scale that cont ...
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. The only
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
that has retained the enlarged ventral scales is the sea kraits, ''
Laticauda Sea kraits are a genus of venomous elapid sea snakes (subfamily: Laticaudinae), ''Laticauda''. They are semiaquatic, and retain the wide ventral scales typical of terrestrial snakes for moving on land, but also have paddle-shaped tails for swimmi ...
'', 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. ''Laticauda'' species are also the only sea snakes with
internasal scales In snakes, the internasal scales are those on top of the head between the scales that surround the nostrils. Wright AH, Wright AA (1957). ''Handbook of Snakes of the United States and Canada''. Ithaca and London: Comstock Publishing Associates. (7t ...
; that is, their nostrils are not located dorsally. Since a snake's tongue can fulfill its 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 The rostral scale, or rostral, in snakes and other scaled reptiles is the median plate on the tip of the snout that borders the mouth opening. Wright AH, Wright AA (1957). ''Handbook of Snakes of the United States and Canada''. Ithaca and London: ...
. 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. Most species of sea snakes are able to 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 The yellow-bellied sea snake (''Hydrophis platurus'') is a venomous species of snake from the subfamily Hydrophiinae (the sea snakes) found in tropical oceanic waters around the world except for the Atlantic Ocean. For many years, it was place ...
'' (a
pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...
species), have shown this species can satisfy about 25% of its oxygen requirements in this manner, which allows for prolonged dives.Campbell JA, Lamar WW. 2004. The Venomous Reptiles of the Western Hemisphere. Comstock Publishing Associates, Ithaca and London. 870 pp. 1500 plates. . 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, and 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. 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 ''Aipysurus'' is a genus of venomous snakes in the subfamily Hydrophiinae of the family Elapidae. Member species of the genus are found in warm seas from the Indian Ocean to the Pacific Ocean. Taxonomy The first description of the genus ''A ...
'', do have imbricate scales to protect against the sharp coral. The scales themselves may be smooth, 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.


Sensory abilities

Vision Vision, Visions, or The Vision may refer to: Perception Optical perception * Visual perception, the sense of sight * Visual system, the physical mechanism of eyesight * Computer vision, a field dealing with how computers can be made to gain un ...
,
chemoreception A chemoreceptor, also known as chemosensor, is a specialized sensory receptor which transduces a chemical substance (endogenous or induced) to generate a biological signal. This signal may be in the form of an action potential, if the chemorecept ...
(tongue-flicking), and
hearing Hearing, or auditory perception, is the ability to perceive sounds In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psycholog ...
are important senses for terrestrial snakes, but these
stimuli A stimulus is something that causes a physiological response. It may refer to: * Stimulation ** Stimulus (physiology), something external that influences an activity ** Stimulus (psychology), a concept in behaviorism and perception * Stimulus (eco ...
become distorted in water. 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. Relatively little is known about sea snake vision. A study of photoreceptors in the
retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...
of spine-bellied, '' Lapemis curtus,'' and horned, ''
Acalyptophis peronii ''Hydrophis peronii'', commonly known as the horned sea snake, Peron's sea snake, and the spiny-headed seasnake, is a species of venomous snake in the subfamily Hydrophiinae of the family Elapidae. The species is endemic to the western tropic ...
'', sea snakes found three classes of
opsin Animal opsins are G-protein-coupled receptors and a group of proteins made light-sensitive via a chromophore, typically retinal. When bound to retinal, opsins become Retinylidene proteins, but are usually still called opsins regardless. Most pro ...
s all from
cone cell Cone cells, or cones, are photoreceptor cells in the retinas of vertebrate eyes including the human eye. They respond differently to light of different wavelengths, and the combination of their responses is responsible for color vision. Cone ...
s. Despite the absence of
rod cell Rod cells are photoreceptor cells in the retina of the eye that can function in lower light better than the other type of visual photoreceptor, cone cells. Rods are usually found concentrated at the outer edges of the retina and are used in per ...
s in sea snake eyes, Simeos ''et al.'' found the
rhodopsin Rhodopsin, also known as visual purple, is a protein encoded by the RHO gene and a G-protein-coupled receptor (GPCR). It is the opsin of the rod cells in the retina and a light-sensitive receptor protein that triggers visual phototransduction ...
(''rh1''), the opsin of the rods, still expressed 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 Vibration is a mechanical phenomenon whereby oscillations occur about an equilibrium point. The word comes from Latin ''vibrationem'' ("shaking, brandishing"). The oscillations may be periodic function, periodic, such as the motion of a pendulum ...
s and chemoreception may be important. One study identified small sensory organs on the head of '' Lapemis curtus'' similar to the mechanoreceptors in
alligator An alligator is a large reptile in the Crocodilia order in the genus ''Alligator'' of the family Alligatoridae. The two extant species are the American alligator (''A. mississippiensis'') and the Chinese alligator (''A. sinensis''). Additiona ...
s and aquatic snake Acrochodus that are used to sense the movement of fish prey. Westhoff ''et al.'' recorded auditory brain responses to
vibration Vibration is a mechanical phenomenon whereby oscillations occur about an equilibrium point. The word comes from Latin ''vibrationem'' ("shaking, brandishing"). The oscillations may be periodic function, periodic, such as the motion of a pendulum ...
underwater in ''Lapemis curtus'', which are sensitive enough to detect movement in prey, but were not as sensitive as fish lateral line systems. Similarly, vision appears to be of limited importance for finding mates. Shine experimented with applying skin secretions (
pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...
s) to snake-like objects to see if male turtle-headed sea snakes, ''
Emydocephalus annulatus ''Emydocephalus annulatus'', commonly known as the turtleheaded sea snake or egg-eating sea snake, is a species of sea snake that can be found in waters of Oceania near Australia and some Pacific Islands such as the Philippines and the Loyalt ...
,'' are attracted to female pheromones. Shine found that although vision may be useful over short distances (less than ), pheromones are more important once the male comes in physical contact with an object. 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. laevis'' possibly is not unique among sea snakes in this respect. Other unique senses, such as electromagnetic reception and
pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
detection, have been proposed for sea snakes, but scientific studies have yet to be performed to test these senses.


Distribution and habitat

Sea snakes are mostly confined to the warm
tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...
waters of the
Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by th ...
and the western
Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...
, with a few species found well out into
Oceania Oceania (, , ) is a region, geographical region that includes Australasia, Melanesia, Micronesia, and Polynesia. Spanning the Eastern Hemisphere, Eastern and Western Hemisphere, Western hemispheres, Oceania is estimated to have a land area of ...
.U.S. Navy. 1991. Poisonous Snakes of the World. US Govt. New York: Dover Publications Inc. 203 pp. . 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. It extends from the east coast of
Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
, from
Djibouti Djibouti, ar, جيبوتي ', french: link=no, Djibouti, so, Jabuuti officially the Republic of Djibouti, is a country in the Horn of Africa, bordered by Somalia to the south, Ethiopia to the southwest, Eritrea in the north, and the Red ...
in the north to
Cape Town Cape Town ( af, Kaapstad; , xh, iKapa) is one of South Africa's three capital cities, serving as the seat of the Parliament of South Africa. It is the legislative capital of the country, the oldest city in the country, and the second largest ...
in the south,Spawls S, Branch B. 1995. The Dangerous Snakes of Africa. Ralph Curtis Books. Dubai: Oriental Press. 192 pp. . across the Indian Ocean, the Pacific, south as far as the northern coast of
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
, all the way to the western coast of the
Americas The Americas, which are sometimes collectively called America, are a landmass comprising the totality of North and South America. The Americas make up most of the land in Earth's Western Hemisphere and comprise the New World. Along with th ...
, where it occurs from northern
Peru , image_flag = Flag of Peru.svg , image_coat = Escudo nacional del Perú.svg , other_symbol = Great Seal of the State , other_symbol_type = Seal (emblem), National seal , national_motto = "Fi ...
in the south (including the
Galápagos Islands The Galápagos Islands (Spanish: , , ) are an archipelago of volcanic islands. They are distributed on each side of the equator in the Pacific Ocean, surrounding the centre of the Western Hemisphere, and are part of the Republic of Ecuador ...
) to the
Gulf of California The Gulf of California ( es, Golfo de California), also known as the Sea of Cortés (''Mar de Cortés'') or Sea of Cortez, or less commonly as the Vermilion Sea (''Mar Bermejo''), is a marginal sea of the Pacific Ocean that separates the Baja Ca ...
in the north. Isolated specimens have been found as far north as
San Diego San Diego ( , ; ) is a city on the Pacific Ocean coast of Southern California located immediately adjacent to the Mexico–United States border. With a 2020 population of 1,386,932, it is the List of United States cities by population, eigh ...
and
Oxnard Oxnard () is a city in Ventura County, California, United States. On California's South Coast, it is the most populous city in Ventura County and the 22nd-most-populous city in California. Incorporated in 1903, Oxnard lies approximately west ...
in the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
. Sea snakes do not occur in the
Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...
. ''Pelamis'' possibly would be found there were it not for the cold currents off
Namibia Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and ea ...
and western
South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...
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 The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; T ...
, believed to be due to its increased salinity, so no danger exists of them crossing through the
Suez Canal The Suez Canal ( arz, قَنَاةُ ٱلسُّوَيْسِ, ') is an artificial sea-level waterway in Egypt, connecting the Mediterranean Sea to the Red Sea through the Isthmus of Suez and dividing Africa and Asia. The long canal is a popular ...
. A lack of salinity is also thought to be the reason why ''Pelamis'' has not crossed into the
Caribbean The Caribbean (, ) ( es, El Caribe; french: la Caraïbe; ht, Karayib; nl, De Caraïben) is a region of the Americas that consists of the Caribbean Sea, its islands (some surrounded by the Caribbean Sea and some bordering both the Caribbean Se ...
via the
Panama Canal The Panama Canal ( es, Canal de Panamá, link=no) is an artificial waterway in Panama that connects the Atlantic Ocean with the Pacific Ocean and divides North and South America. The canal cuts across the Isthmus of Panama and is a conduit ...
. Despite their marine adaptations, most sea snakes prefer shallow waters near land, around islands, and especially somewhat sheltered waters, as well as near estuaries. They may swim up rivers and have been reported as far as from the sea. Others, such as ''P. platurus'', are
pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...
and are found in drift lines, slicks of floating debris brought together by surface currents.The sea snakes are coming
a
NewScientist
Accessed 13 January 2009.
Some sea snakes inhabit mangrove swamps and similar brackishwater habitats, and two landlocked freshwater forms are found: ''
Hydrophis semperi ''Hydrophis semperi'', commonly known as the Lake Taal snake, Garman's sea snake, the Philippine freshwater sea snake, and the Luzon sea snake, is a rare species of venomous sea snake found only in a single lake on the island of Luzon in the Ph ...
'' occurs in
Lake Taal Taal Lake ( tl, Lawa ng Taal, ), formerly known as Bombón Lake, is a freshwater caldera lake in the province of Batangas, on the island of Luzon in the Philippines. The lake fills Taal Volcano, a large volcanic caldera formed by very large ...
in the
Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...
, and '' Laticauda crockeri'' in Lake Te Nggano on
Rennell Island Rennell Island, locally known as Mugaba, is the main island of two inhabited islands that make up the Rennell and Bellona Province in the nation state of Solomon Islands. Rennell Island has a land area of that is about long and wide. It is th ...
in the
Solomon Islands Solomon Islands is an island country consisting of six major islands and over 900 smaller islands in Oceania, to the east of Papua New Guinea and north-west of Vanuatu. It has a land area of , and a population of approx. 700,000. Its capita ...
.


Behavior

Sea snakes are generally reluctant to bite, and are usually considered to be mild-tempered, although variation is seen among species and individuals. 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. Species reported as much more aggressive include '' Aipysurus laevis'', '' Astrotia stokesii'', '' Enhydrina schistosa'', '' Enhydrina zweifeli'', and ''
Hydrophis ornatus ''Hydrophis ornatus'', commonly known as the ornate reef sea snake, is a species of venomous sea snake in the family Elapidae. Distribution This snake-species is found to occur in Andaman & Nicobar Islands, Bahrain, Bangladesh, Cambodia, C ...
''. 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. 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. They have been reported swimming at depths over , and can remain submerged for as long as a few hours, possibly depending on temperature and degree of activity. Sea snakes have been sighted in huge numbers. For example, in 1932, a steamer in the
Strait of Malacca The Strait of Malacca is a narrow stretch of water, 500 mi (800 km) long and from 40 to 155 mi (65–250 km) wide, between the Malay Peninsula (Peninsular Malaysia) to the northeast and the Indonesian island of Sumatra to the southwest, connec ...
, off the coast of
Malaysia Malaysia ( ; ) is a country in Southeast Asia. The federation, federal constitutional monarchy consists of States and federal territories of Malaysia, thirteen states and three federal territories, separated by the South China Sea into two r ...
, reported sighting "millions" of '' Astrotia stokesii'', a relative of ''Pelamis''; these reportedly formed a line of snakes wide and long. The cause of this phenomenon is unknown, although it likely has to do with reproduction. They can sometimes be seen swimming in schools of several hundred, and many dead specimens have been found on beaches after typhoons.


Ecology

They feed on small fish and occasionally young octopus. They are often associated with the sea snake barnacle (''Platylepas ophiophila''), which attaches to their skin.


Reproduction

Except for a single genus, all sea snakes are
ovoviviparous Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a term used as a "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparous reproduction. Ovoviviparous animals possess embryos that develop insi ...
; the young are born alive in the water where they live their entire lives. In some species, the young are quite large, up to half as long as the mother. The one exception is the genus ''Laticauda'', which is oviparous; its five species all lay their eggs on land.


Venom

Like their relatives in the family Elapidae, the majority of the sea snakes are highly venomous, but rarely inject it when biting, so such damage to humans seems nonexistent or trivial. For example, ''
Hydrophis platurus The yellow-bellied sea snake (''Hydrophis platurus'') is a venomous species of snake from the subfamily Hydrophiinae (the sea snakes) found in tropical oceanic waters around the world except for the Atlantic Ocean. For many years, it was place ...
'' has a venom more potent than any terrestrial snake species in
Costa Rica Costa Rica (, ; ; literally "Rich Coast"), officially the Republic of Costa Rica ( es, República de Costa Rica), is a country in the Central American region of North America, bordered by Nicaragua to the north, the Caribbean Sea to the no ...
based on LD50, but despite its abundance in the waters off its western coast, few human fatalities have been reported. 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. 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 A lymph node, or lymph gland, is a kidney-shaped organ of the lymphatic system and the adaptive immune system. A large number of lymph nodes are linked throughout the body by the lymphatic vessels. They are major sites of lymphocytes that inclu ...
s affected. The most important symptoms are
rhabdomyolysis Rhabdomyolysis (also called rhabdo) is a condition in which damaged skeletal muscle breaks down rapidly. Symptoms may include muscle pains, weakness, vomiting, and confusion. There may be tea-colored urine or an irregular heartbeat. Some of th ...
(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 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 Trismus, commonly called ''lockjaw'' as associated with tetanus, is a condition of limited jaw mobility. It may be caused by spasm of the muscles of mastication or a variety of other causes. Temporary trismus occurs much more frequently than perma ...
, which is similar to
tetanus Tetanus, also known as lockjaw, is a bacterial infection caused by ''Clostridium tetani'', and is characterized by muscle spasms. In the most common type, the spasms begin in the jaw and then progress to the rest of the body. Each spasm usually ...
, is common. This is followed later on by symptoms typical of other
elapid Elapidae (, commonly known as elapids ; grc, ἔλλοψ ''éllops'' "sea-fish") is a family of snakes characterized by their permanently erect fangs at the front of the mouth. Most elapids are venomous, with the exception of the genus Emydoce ...
envenomations, a progressive flaccid paralysis, starting with ptosis and paralysis of voluntary muscles. Paralysis of muscles involved in swallowing and respiration can be fatal.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. . Vick ''et al'' (1975) estimated that the LD50 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. In this regard, recall the recent report by Ishikawa ''et al'' (1985) indicating a substantially lower binding affinity between sea snake neurotoxin and human and chimpanzee 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 In the kidney, the loop of Henle () (or Henle's loop, Henle loop, nephron loop or its Latin language, Latin counterpart ''ansa nephroni'') is the portion of a nephron that leads from the proximal convoluted tubule to the distal convoluted tubule. ...
, 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.


Taxonomy

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 genera with 64 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.


Molecular studies

Molecular data studies suggest all three monotypic semiaquatic genera (''
Ephalophis Grey's mudsnake (''Ephalophis greyae''), also known commonly as the mangrove seasnake, is a species of venomous snake in the subfamily Hydrophiinae of the family Elapidae. The species is endemic to northwestern Australia. Etymology Its specific ...
'', '' Parahydrophis'' and ''
Hydrelaps ''Hydrelaps'' is a monotypic genus of venomous sea snake in the family Elapidae. The genus contains the sole species ''Hydrelaps darwiniensis'', also commonly known as the black-ringed mangrove snake, the black-ringed sea snake, Darwin's sea snak ...
'') are early diverging lineages.


Captivity

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. Over 50 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 Sea kraits are a genus of venomous elapid sea snakes (subfamily: Laticaudinae), ''Laticauda''. They are semiaquatic, and retain the wide ventral scales typical of terrestrial snakes for moving on land, but also have paddle-shaped tails for swimmi ...
'' species need to be able to exit the water somewhere at about , along with a submerged shelter. Species that have done relatively well in captivity include the ringed sea snake, ''
Hydrophis cyanocinctus ''Hydrophis cyanocinctus'', commonly called the annulated sea snake or the blue-banded sea snake, is a species of venomous sea snake in the family Elapidae. Description Head moderate. Diameter of eye less than its distance from the mouth in the ...
'', which feeds on
fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
and
eel Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 19 families, 111 genera, and about 800 species. Eels undergo considerable development from the early larval stage to the eventual adult stage ...
s in particular. '' Pelamis platurus'' has done especially well in captivity, accepting small fish, including
goldfish The goldfish (''Carassius auratus'') is a freshwater fish in the family Cyprinidae of order Cypriniformes. It is commonly kept as a pet in indoor aquariums, and is one of the most popular aquarium fish. Goldfish released into the wild have ...
. Housing them in round tanks, or in rectangular tanks with well-rounded corners, prevents snakes from damaging their snouts on the sides.


Conservation status

Most sea snakes are not on the
CITES CITES (shorter name for the Convention on International Trade in Endangered Species of Wild Fauna and Flora, also known as the Washington Convention) is a multilateral treaty to protect endangered plants and animals from the threats of interna ...
protection lists.Serpentes
a
CITES
Accessed 11 August 2007.
One species, '' Laticauda crockeri'', is classified as vulnerable. Several species of ''
Aipysurus ''Aipysurus'' is a genus of venomous snakes in the subfamily Hydrophiinae of the family Elapidae. Member species of the genus are found in warm seas from the Indian Ocean to the Pacific Ocean. Taxonomy The first description of the genus ''A ...
'' are listed with conservation status of greater concern, the Timor species '' A. fuscus'' is known to be endangered, and two others found in seas north of Australia, the leaf-scaled '' A. foliosquama'' and short-nosed '' A. apraefrontalis'', are classified as critically endangered according to the
IUCN The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...
Red List of Threatened Species.


See also

*
List of marine reptiles Following is a list of marine reptiles, reptiles which are adapted to life in marine or brackish environments. Extant The following marine reptiles are species which are currently extant or recently extinct. Crocodiles :*'' Crocodylus'' ::' ...
*
Snakebite A snakebite is an injury caused by the bite of a snake, especially a venomous snake. A common sign of a bite from a venomous snake is the presence of two puncture wounds from the animal's fangs. Sometimes venom injection from the bite may occu ...
*
Sea serpent A sea serpent or sea dragon is a type of dragon sea monster described in various mythologies, most notably Mesopotamian (Tiamat), Judaeo-Christian (Leviathan), Greek (Cetus, Echidna, Hydra, Scylla), and Norse (Jörmungandr). Mythology and fo ...


References


Further reading

* 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
PDF
at the ournal 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.


External links


Sea Snakes in AustraliaSea Snakes
a
Scubadoc's Diving Medicine Online
Accessed 6 August 2007.
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 {{Authority control Taxa named by Malcolm Arthur Smith