Sea snake

This is a good article. Click here for more information.
Source: Wikipedia, the free encyclopedia.
(Redirected from
Sea snakes
)

Sea snake
Temporal range: Oligocene – Recent[1]
Yellow-bellied sea snake (Hydrophis platurus) on a beach in Costa Rica
Yellow-bellied sea snake (
Hydrophis platurus
) on a beach in Costa Rica
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Suborder: Serpentes
Superfamily: Elapoidea
Family: Elapidae
Groups included
Range of sea snakes shown in lime green, except the widespread, pelagic yellow-bellied sea snake
Range of sea snakes shown in lime green, except the widespread, pelagic yellow-bellied sea snake

Sea snakes, or coral reef snakes, are

marine environments for most or all of their lives. They belong to two subfamilies, Hydrophiinae and 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 between seven genera.[2]

Most sea snakes are

Pacific and are closely related to venomous terrestrial snakes in Australia.[4]

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 gills and must surface regularly to breathe. Along with Cetaceans, they are among the most completely aquatic of all extant air-breathing vertebrates.[5] Among this group are species with some of the most potent venoms of all snakes. 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 120 and 150 cm (4 and 5 ft) in length,[6] with the largest, Hydrophis spiralis, reaching a maximum of 3 m (10 ft).[7] Their eyes are relatively small with a round pupil[8] and most have nostrils located dorsally.[9] 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.[5]

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.

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.[6][9]

The only

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.[6][9] Laticauda species are also the only sea snakes with internasal scales; that is, their nostrils are not located dorsally.[10]

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.[5] 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.[6][9]

Most species of sea snakes are able to

pelagic species), have shown this species can satisfy about 25% of its oxygen requirements in this manner, which allows for prolonged dives.[11]

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, 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.[5][9]

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, 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.[9]

Sensory abilities

Vision, chemoreception (tongue-flicking), and hearing are important senses for terrestrial snakes, but these stimuli become distorted in water.[12][13] 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.[14]

Relatively little is known about sea snake vision. A study of

Acrochodus that are used to sense the movement of fish prey.[20] Westhoff et al. recorded auditory brain responses to vibration underwater in Lapemis curtus,[21] 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 (pheromones) 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 1 m [3 ft]), pheromones are more important once the male comes in physical contact with an object.[22]

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.[23]

Other unique senses, such as electromagnetic reception and pressure detection,[24] have been proposed for sea snakes, but scientific studies have yet to be performed to test these senses.[14]

Distribution and habitat

Sea snakes are mostly confined to the warm

San Diego and Oxnard in the United States.[28]

Sea snakes do not occur in the Atlantic Ocean.[9] 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.[5]

Despite their marine adaptations, most sea snakes prefer shallow waters near land, around islands, and especially somewhat sheltered waters, as well as near estuaries.

Laticauda crockeri in Lake Te Nggano on Rennell Island in the Solomon Islands.[9]

Behavior

Sea snakes are generally reluctant to bite,

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.[7][8]

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.[6] They have been reported swimming at depths over 90 m (300 ft), and can remain submerged for as long as a few hours, possibly depending on temperature and degree of activity.[7][25]

Sea snakes have been sighted in huge numbers. For example, in 1932, a steamer in the

Astrotia stokesii, a relative of Pelamis; these reportedly formed a line of snakes 3 m (10 ft) wide and 100 km (60 mi) long.[29] The cause of this phenomenon is unknown, although it likely has to do with reproduction.[5] They can sometimes be seen swimming in schools of several hundred, and many dead specimens have been found on beaches after typhoons.[8]

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.[30]

Reproduction

Except for a single genus, all sea snakes are

oviparous; its five species all lay their eggs on land.[9]

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.

LD50, but despite its abundance in the waters off its western coast, few human fatalities have been reported.[11] 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.[31]

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 nodes 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 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 elapid envenomations, a progressive flaccid paralysis, starting with ptosis and paralysis of voluntary muscles. Paralysis of muscles involved in swallowing and respiration can be fatal.[32]

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

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.[33]

Taxonomy

Cladogram
Elapidae

Cobra

Hydrophiinae
sea kraits

Laticauda

Notechis

other sea snakes

Emydocephalus

Aipysurus

Hydrelaps

Hydrophis

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.

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.[34][2][8][9][4]

Genus[2] Taxon authority[34] Species[2] Subsp.[34][a] Common name[35] Geographic range[35]
Aipysurus
Lacépède
, 1804
9 1 olive sea snakes
Loyalty Islands, southern New Guinea, Indonesia, western Malaysia and Vietnam
Emydocephalus Krefft, 1869 3 0 turtlehead sea snakes the coasts of Timor (Indonesian Sea), New Caledonia, Australia (Northern Territory, Queensland, Western Australia), and in the Southeast Asian sea along the coasts of China, Taiwan, Japan, and the Ryukyu Islands
Ephalophis
M.A. Smith, 1931 1 0 Grey's mudsnake northwestern Australia
Hydrelaps Boulenger, 1896 1 0 Port Darwin mudsnake northern Australia, southern New Guinea
Hydrophis Latreille in Sonnini & Latreille, 1801 49 3 sea snakes Indo-Australian and Southeast Asian waters.[36]
Laticauda
Laurenti, 1768 8 0 sea kraits Southeast Asian and Indo-Australian waters
Parahydrophis
Burger & Natsuno, 1974 1 0 northern mangrove sea snake northern Australia, southern New Guinea
  1. ^ Not counting the nominate subspecies

Molecular studies

Molecular data studies suggest all three monotypic semiaquatic genera (

Parahydrophis and Hydrelaps) are early diverging lineages.[37]

Captivity

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.

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.[9]

Conservation status

Most sea snakes are not on the

IUCN Red List of Threatened Species.[39]

See also

References

  1. ISSN 1323-1650
    .
  2. ^ a b c d Uetz, P.; Freed, P.; Aguilar, R.; Hošek, J., eds. (2022). "Elapidae". The Reptile Database. Retrieved 9 May 2022.
  3. PMID 6658813
    .
  4. ^ . 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.
  5. ^ (paper).
  6. ^ .
  7. ^ .
  8. ^ a b c d e Ditmars RL. 1933. Reptiles of the World. Revised Edition. The MacMillan Company. 329 pp. 89 plates.
  9. ^ .
  10. ^ a b c d e f g Rasmussen, A.R. (2001). "Sea snakes". In Kent E. Carpenter; Volker H. Niem (eds.). The living marine resources of the Western Central Pacific. FAO species identification guide for fishery purposes. Rome: Food and Agriculture Organization of the United Nations. pp. 3987–4008. Archived from the original (PDF) on 6 February 2019. Retrieved 7 August 2007.
  11. ^ .
  12. .
  13. .
  14. ^ .
  15. .
  16. .
  17. ^ Heatwole, H; Cogger, H (1993). Fauna of Australia (PDF). Canberra, Australia: AGPS. p. 16.
  18. .
  19. . Retrieved 2 April 2016.
  20. .
  21. .
  22. .
  23. .
  24. .
  25. ^ .
  26. .
  27. .
  28. ^ "Venomous Yellow-Bellied Sea Snake Washes Up on Coronado Beach".
  29. ^ a b The sea snakes are coming at NewScientist. Accessed 13 January 2009.
  30. .
  31. ^ Smith, Emily (8 October 2018). "Fisherman's deadly encounter with sea snake incredibly rare". ABC News.
  32. .
  33. .
  34. ^ a b c "Elapidae". Integrated Taxonomic Information System. Retrieved 7 August 2007.
  35. ^ a b Elapidae Archived 2008-10-11 at the Wayback Machine at the New Reptile Database. Accessed 12 August 2007.
  36. ^ The Hydrophiidae at Cyberlizard's home pages. Accessed 12 August 2007.
  37. PMID 23026811
    .
  38. ^ Serpentes Archived 2020-05-30 at the Wayback Machine at CITES. Accessed 11 August 2007.
  39. ^ "Red list search". IUCN Red List. Archived from the original on 6 November 2009. Retrieved 16 June 2023.

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 [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.

External links