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Yellowbelly (Pelagic) Sea Snake - Pelamis platurus
Yellowbelly (Pelagic) Sea Snake - Pelamis platurus

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Scientific classification 
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Suborder: Serpentes
Family: Elapidae
Genus: Hydrophis
Species: Hydrophis (Pelamis) platurus

Conservation Status: Least Concern

The Yellowbelly Sea Snake or Pelagic Sea Snake (Pelamis platurus) is a species of sea snake found in tropical oceanic waters around the world. It is the only member of the genus Pelamis.

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Body compressed, posteriorly more than twice the diameter of the neck; body scales juxtaposed, sub-quadrangular in shape, in 49-67 rows around thickest part of body; ventral scales, 264-406, very small and, if distinct, divided by a longitudinal groove, but usually indistinguishable from adjacent body scales; head narrow, snout elongate, head shields entire, nostrils superior, nasal shields in contact with one another; pre-frontal in contact with second upper labial; 1-2 pre- and 2-3 post-oculars; 2-3 small anterior temporals; 7-8 upper labials, 4-5 below eye but separated from border by sub-ocular; color variable but most often distinctly bi-colored, black above, yellow or brown below, the dorsal and ventral colors sharply demarcated from one another; ventrally there may be a series of black spots or bars on the yellow or brown background, or the yellow may extend dorsally so that there is only a narrow mid-dorsal black stripe, or a series of black crossbars (M A Smith 1943:476-477 gives more complete description of the color pattern variants). Total length males 720 mm, females 880 mm; tail length males 80 mm, females 90 mm.

These snakes breed in warm waters and they are ovoviviparous with a gestation period of about 6 months. They are helpless on land and they sometimes form large aggregations of thousands in surface waters. The snake has a neurotoxic venom that is used against its fish prey. No human fatalities are known.

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The yellowbelly is the most widely distributed sea snake and is capable of living and giving birth entirely in the open sea (it is totally pelagic), being found in all coastal waters around the rim of the Pacific Ocean except Alaska south to southern California, and in the coastal waters of the Indian Ocean from the Persian Gulf eastwards. It is the only sea snake to have reached the Hawaiian Islands.

Yellowbellies (and all other sea snakes) are not found in the Atlantic or Mediterranean even though the water there is warm enough. Yellowbellies require a minimum of 16-18° C to survive long term (Dunson and Ehlert 1971). Yellowbellies have not gone around the southern tips of South America or South Africa because water temperatures are too cool.

A land bridge formed (at Panama) between North and South America about 3 million years ago, making it impossible for them to enter the Caribbean Sea from the Pacific. If they had reached the eastern Pacific Ocean before the land bridge formed, we would almost certainly find them now in the Atlantic. The Panama canal has not made a crossing of the isthmus possible because it is freshwater.

They do not live in the Red Sea because of its excessive salinity.

The yellowbelly seems to have evolved from the terrestrial elapids of Asia and Australia about 10 million years ago. This air breathing sea snake has developed a flat oar-like tail and valved nostrils since leaving the land millions of years ago.

Sea snakes are closely related to the venomous Australian snakes of the family Elapidae, but are currently classified in a separate family, Hydrophiidae. Two subfamilies have been listed in the past, the sea kraits (Laticaudinae), and the true sea snakes (Hydrophiinae), though recent work suggests this subfamilial division may be inappropriate.

In 1766, Linnaeus referred to the yellow-bellied sea snake as 'Anguis platura' (Anguis meaning snake). Daudin referred to it as 'Pelamis platuros' in 1803 and usually has his name attached to the spelling 'Pelamis platurus' which people are now familiar with. In 1842 Gray transferred it to the genus Pelamis and called it 'Pelamis ornata' (ornata being a synonym of platura). The word 'Pelamis' is a feminine noun and means young or small tunny fish. In 1872 Stoliczka introduced the name 'Pelamis platurus' (still the most used scientific name by scientists today) but used the incorrect ending on 'platurus' instead of 'platura' which a feminine noun requires. There are a few recent examples where scientists have begun using the grammatically correct name 'Palamis platura' eg. Bohme 2003 and the 'Reptile database' with its page headed 'Pelamis platura' Linnaeus, 1766' which gives a huge variety of different scientific names for the yellowbelly sea snake.

The genus name Pelamis is derived from the Ancient Greek word for "tunny fish", which presumably refers to the habitat or what Daudin thought they ate. The species name platurus' is a combination of the Ancient Greek words platys "flat" and oura "tail", referring to the flattened tail.

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Though its venom is highly potent, Pelamis platurus poses a lesser threat than other snakes, like the Inland Taipan. Even though the toxicity of yellow-bellied sea snake venom is about a quarter that of the beaked sea snake, it is still potentially lethal. " The yellow-bellied sea snake is about 10 times more venomous than the Egyptian cobra (Naja haje) but it delivers a much smaller quantity of venom. In Australia sea-snakes are rarely aggressive and bites are uncommon. The venomousness of Pelamis platurus is: Mouse LD50 (mg/kg) : 0.07 Venom yield per snake (mg) : 1.0-4.0 Below is the comparative venomousness of the other snakes mentioned:

Hook-nosed sea snake or beaked sea snake (Enhydrina schistosa) Mouse LD50 (mg/kg) : 0.02. Venom yield per snake (mg) : 7.7-9.0 (generally considered to be the most venomous sea snake in the world).
Inland Taipan (Oxyuranus microlepidotus) Mouse LD50 (mg/kg) : 0.03. Venom yield per snake (mg) : 44.0-110.0 (generally considered to be the most venomous land snake).
Egyptian cobra (Naja haje) Mouse LD50 (mg/kg) : 0.19. Venom yield per snake (mg) : 175.0-300.0.

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Anti-venom (antivenin)
Sea snake venom can cause damage to skeletal muscle with consequent myoglobinuria, neuromuscular paralysis or direct renal damage. The venoms of significant species of sea snake are neutralised with Commonwealth Serum Laboratories Ltd (of Melbourne, Australia) Sea Snake (Enhydrina schistosa) antivenom. If that preparation is not available, Tiger Snake or polyvalent antivenom should be used. No deaths have been recorded from bites in Australian waters. The (Enhydrina schistosa) antivenom was tested specifically on Pelamus platurus and it effectively neutralised the venom.

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Camels of the Ocean: Sea Snake Dehydrates for Months

By Tia Ghose, Staff Writer | March 18, 2014 08:01pm ET

A yellow-bellied sea snake on the beach in Costa Rica

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Like camels of the sea, a species of sea snake goes without a drink for months on end, gradually dehydrating, before refueling with freshwater when rain falls, new research suggests.

"Perhaps six or seven months of the year, these snakes are living thirsty," said Coleman Sheehy III, an evolutionary biologist at the University of Florida, and a co-author of the study published today (March 18) in the journal Proceedings of the Royal Society B.

Marine snake

Past studies have found that snakes can dehydrate for short periods of time and then gulp freshwater when it's available, but those snakes typically have access to freshwater sources such as nearby springs. 

The yellow-bellied sea snake, Hydrophis platurus, by contrast, has a vast range and habitat. The 3.3-foot-long (1 meter) snakes drift along ocean currents feeding on fish, and are found in the middle of the vast Indian and Pacific oceans, spending months without any freshwater sources.

To understand exactly how they manage this feat, Sheehy and his colleagues gingerly collected hundreds of the wild sea snakes in the Guanacaste province of Costa Rica. (The sea snakes have a nasty, venomous bite, though no one has died from one, Sheehy said.) In that region, the dry season lasts from December to May or June, and the snakes were collected on several different trips at different points in both seasons.

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H. platurus, or the yellow-bellied sea snake, drifts along ocean currents and can live far out to sea.

They then took the snakes back to their lab, towel-dried them, and measured and weighed them.

Next, they placed the snakes in freshwater tanks to see whether the sea creatures drank.

Snakes collected after long dry spells were extremely skinny, because they had been slowly drying out. The slimmest snakes also drank freshwater in the lab aquariums, plumping up and rehydrating.

But many snakes collected during the rainy season and shortly afterward didn't sip a drop of water, suggesting they can go quite a while, even one to two months, before they get the urge to rehydrate.

"They tank up during the rainy season and then it takes a while for them to get thirsty enough to drink," Sheehy told Live Science.

The team suspects that H. platurus has evolved adaptations to prevent freshwater loss through the skin.

But at some point, the sea snakes need to drink, so where do they get their water?

"The only source of freshwater for a marine snake like this species that's living in the middle of the ocean is rainfall," Sheehy said.

During rainy periods, the rainfall floats at the top of the denser saltwater ocean and accumulates in layers known as freshwater lenses. It's these freshwater lenses that provide a drink for the parched yellow-bellied sea snake.

The snakes are hardwired to come up to the surface to drink, even when they are in a freshwater aquarium where a good drinking source is all around them, Sheehy said. 

The new study shows that animals that evolved on land but then moved into the seas have developed a unique array of adaptations to their salty home. For instance, whales seals, sea turtles and other animals have evolved not to need any freshwater access at all — either by having salt glands that process seawater, or by extracting water from their food, Sheehy said. 

"Instead of adapting to marine environments like many other vertebrates have, these animals, sea snakes, have taken a different approach," Sheehy said.

Pelagic sea snakes dehydrate at sea

Harvey B. Lillywhite, Coleman M. Sheehy, François Brischoux and Alana Grech
Proc. R. Soc. B 7 May 2014 vol. 281 no. 1782 20140119

Secondarily marine vertebrates are thought to live independently of fresh water. Here, we demonstrate a paradigm shift for the widely distributed pelagic sea snake, Hydrophis (Pelamis) platurus, which dehydrates at sea and spends a significant part of its life in a dehydrated state corresponding to seasonal drought. Snakes that are captured following prolonged periods without rainfall have lower body water content, lower body condition and increased tendencies to drink fresh water than do snakes that are captured following seasonal periods of high rainfall. These animals do not drink seawater and must rehydrate by drinking from a freshwater lens that forms on the ocean surface during heavy precipitation. The new data based on field studies indicate unequivocally that this marine vertebrate dehydrates at sea where individuals may live in a dehydrated state for possibly six to seven months at a time. This information provides new insights for understanding water requirements of sea snakes, reasons for recent declines and extinctions of sea snakes and more accurate prediction for how changing patterns of precipitation might affect these and other secondarily marine vertebrates living in tropical oceans. 
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Ceratodromeus Wrote:Fom the 2015 herpetological review, comes this neat interaction 

"Hydrophis platura is the only fully pelagic sea snake. It is thought to be predominantly a passive drifter that concentrates around ocean slicks, where it sometimes forms aggregations into the millions (Campbell and Lamar 2004. Venomous Reptiles of the Western Hemisphere. Cornell University Press, Ithaca, New York. 870 pp.). Little is known about biotic interactions of H. platura. It eats fishes and probably has few predators because it is unpalatable to many fishes and may have toxic flesh (Campbell and Lamar, op. cit.). At ~1015 h on 7 November 2013, one of us (EL) was swimming with a pod of about half a dozen Tursiops truncatus (Common Bottlenose Dolphins) in Banderas Bay, Jalisco, Mexico (20.7031078°N, 105.3278205°W; datum WGS84), when two of the dolphins began interacting with an adult H. platura (Fig. 1; total length ca. 70 cm based on photographs). Over a period of 6–7 min, the two dolphins pushed the snake around in the water with their heads and repeatedly threw it into the air using their tails. The snake did not react in any obvious way, only continued to swim. Although wild and captive delphinids occasionally manipulate other animals for functional purposes (e.g., Smolker et al. 1997. Ethology 103:454–465), the majority of reports of these kinds of interactions seem to serve no particular purpose and are categorized as play. Social object play using plants or animals that do not serve as prey often involves pushing these animals around, passing them from one part of the body to another or among individuals, or chasing and grabbing them only to release them before chasing again (Janik 2015. Current Biol. 25:R7–R8). These behaviors are often accompanied by splashing, aerial displays, and social interactions (Mann and Smuts 1999. Behaviour 136:529–566). Because the behavior of the dolphins we observed fit this description, we suggest that the dolphins were playing with the snake. If this was indeed the case, this is the first documentation of dolphins playing with a marine reptile. Dolphins do not appear to prey upon H. platura. Kropach (1972. PhD dissertation, The City University of New York), reporting the unpublished data of other investigators, stated that stomach contents of 214 dolphins examined from areas of the eastern Pacific where H. platura was plentiful contained no sea snakes, and Heatwole (1975. In W. A. Dunson [ed.], The Biology of Sea Snakes, pp. 233–249. University Park Press, Baltimore, Maryland) concluded that H. platura are nearly free from predation. Two reports of pinnipeds, both of which became ill, consuming H. platura suggest that the snakes are unpalatable to marine mammals. In addition, the venom of H. platura is largely neurotoxic and is probably highly potent. Although only a few fatal bites to humans have been reported, the potential for fatal bites to marine mammals exists.
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Ceph Wrote:Highly venomous sea snake seen in California for first time in 30 years

Oct 18th 2015 

A venomous snake species has been spotted in California for the first time in roughly three decades.

As far as the Golden State is concerned, the last known sighting of the yellow-bellied sea snake was in the early 1980s -- in the midst of an El Niño weather event.

With an unusually strong El Niño this year and two sightings reported on a beach in Oxnard, California, scientists are asking for the public's help to confirm whether these warm-water-favoring snakes have actually made landfall.

Heal the Bay, an environmental organization, is encouraging citizens to document any sightings with images and location data.

But whatever you do -- just don't touch them. The yellow-bellied sea snake produces some of the most lethal venom in the world.

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Sea snakes have extra sense for water living

Date: June 8, 2016
Source: University of Adelaide

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The head of a Beaked sea snake (Hydrophis schistosus) and a close up of a single scale on head. Each scale has many 'scale sensilla' that protrude from it's surface, these small organs may allow aquatic snakes to 'feel' their environment. Scale bar, 3 mm.
Credit: Jenna Crowe-Riddell

The move from life on land to life in the sea has led to the evolution of a new sense for sea snakes, a University of Adelaide-led study suggests.

The international team, led by researchers in the University's School of Biological Sciences, studied tiny and poorly understood structures on the heads of snakes called 'scale sensilla'. The research has been published in the Royal Society journal Open Biology.

"Land snakes and many lizards have small raised structures on the scales on their heads -- called scale sensilla -- that they use to sense objects by direct touch," says lead author Jenna Crowe-Riddell, University of Adelaide PhD student.

"We found that the scale sensilla of sea snakes were much more dome-shaped than the sensilla of land snakes, with the organs protruded further from the animals' scales, potentially making them more likely to be able to sense vibrations from all directions. We also found that scale sensilla on some of the fully aquatic snakes covered a much higher proportion of the scales' surface.

"We believe sea snakes use these organs to sense objects at a distance by 'feeling' movements in the water. This hydrodynamic sense is not an option for land animals. In water, a new way of sensing the environment becomes possible."

Sea snakes evolved from land-living snakes, taking to life in the sea between 9 and 20 million years ago. They spend the majority of their lives at sea: hunting fish, swimming and diving using a paddle-shaped tail, and coming up to the water's surface to breathe air. Although they can also see, little is known about the underwater sensory perception of the snakes.

"Every movement of a fin or flipper generates vibrations underwater, like when you drop a stone into a pond and the surrounding ripples spread to every corner of the pond," says Ms Crowe-Riddell.

The researchers, including from the University of Witwatersrand in South Africa and from the University of Western Australia, looked at 19 species of snakes, including fully-aquatic, semi-aquatic and land species, and measured the coverage of sensilla over single scales on their heads.

They used DNA sequencing to reconstruct the evolutionary relationships between the snakes; and used microscope imaging and specially developed software to automatically detect the small organs from silicone casts of snake heads. They also examined the shape of the sensilla using scanning electron microscopy.

"What we now need to do," says lead scientist Dr Kate Sanders, "is to investigate the physiology of these scale sensilla and demonstrate exactly what they can sense. If they are hydrodynamic tactile sense organs, as we suspect, then by comparing them to the scale sensilla of closely related land-snakes we can start to understand how evolution has changed these organs from direct-touch sensors to distance vibration-sensors that work underwater."

The researchers believe being able to sense vibrations underwater would mean potential impacts on sea snake populations from man-derived disturbances such as motor boats and seismic surveys.

Story Source: University of Adelaide. "Sea snakes have extra sense for water living." ScienceDaily. (accessed June 9, 2016).

Journal Reference:
Jenna M. Crowe-Riddell, Edward P. Snelling, Amy P. Watson, Anton Kyuseop Suh, Julian C. Partridge, Kate L. Sanders. The evolution of scale sensilla in the transition from land to sea in elapid snakes. Open Biology, 2016; 6 (6): 160054 DOI: 10.1098/rsob.160054

Scale sensilla are small tactile mechanosensory organs located on the head scales of many squamate reptiles (lizards and snakes). In sea snakes and sea kraits (Elapidae: Hydrophiinae), these scale organs are presumptive scale sensilla that purportedly function as both tactile mechanoreceptors and potentially as hydrodynamic receptors capable of sensing the displacement of water. We combined scanning electron microscopy, silicone casting of the skin and quadrate sampling with a phylogenetic analysis to assess morphological variation in sensilla on the postocular head scale(s) across four terrestrial, 13 fully aquatic and two semi-aquatic species of elapids. Substantial variation exists in the overall coverage of sensilla (0.8–6.5%) among the species sampled and is broadly overlapping in aquatic and terrestrial lineages. However, two observations suggest a divergent, possibly hydrodynamic sensory role of sensilla in sea snake and sea krait species. First, scale sensilla are more protruding (dome-shaped) in aquatic species than in their terrestrial counterparts. Second, exceptionally high overall coverage of sensilla is found only in the fully aquatic sea snakes, and this attribute appears to have evolved multiple times within this group. Our quantification of coverage as a proxy for relative ‘sensitivity’ represents the first analysis of the evolution of sensilla in the transition from terrestrial to marine habitats. However, evidence from physiological and behavioural studies is needed to confirm the functional role of scale sensilla in sea snakes and sea kraits.

Attached to this post:[Image: attach.png] The_evolution_of_scale_sensilla_in_the_transition_from_land_to_sea_in_elapid_snakes.pdf (1.41 MB)
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Sea snakes that can't drink seawater

February 8, 2019 by Rachel Wayne, University of Florida

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The yellow-bellied sea snake (Hydrophis platurus) is the only reptile in the order Squamata that lives on the open sea. Credit: Mark Sandfoss, University of Florida

Surrounded by salty water, sea snakes sometimes live a thirsty existence. Previously, scientists thought that they were able to drink seawater, but recent research has shown that they need to access freshwater. A new study published in PLOS ONE on Feb. 7 and led by Harvey Lillywhite, professor of biology of the University of Florida, shows that sea snakes living where there is drought relieve their dehydration as soon as the wet season hits, and do so by obtaining freshwater from "lenses" that form on the surface of the ocean during heavy rain—events in which the salinity at the surface decreases enough for the water to be drinkable.

The yellow-bellied sea snake (Hydrophis platurus) is the only reptile in the order Squamata that lives on the open sea. It has one of the largest geographic ranges of any vertebrate species. Given its broad range and seafaring existence, during the dry season (6-7 months at the study site in Costa Rica) it has no access to freshwater. How they survive in regions of drought seems to hinge upon access to freshwater lenses, but little is known about how marine vertebrates react to or consume rainfall. "This study contributes to a fuller understanding of how pelagic sea snakes, and possibly other marine animals, avoid desiccation following seasonal drought at sea," said Lillywhite.

The researchers captured 99 sea snakes off the coast of Costa Rica (interestingly, the snakes have never been observed in estuaries) and offered them freshwater in a laboratory environment. The team happened to be there just as six months of drought broke and the rainy season began. They found that only 13 percent of snakes captured after the rainfall began accepted the offer, compared to 80 percent of those captured before. The rainfall must have quenched their thirst.

The study continues many years of work by Lillywhite. The present paper was coauthored by Mark Sandfoss, Lillywhite's current Ph.D. student, Coleman Sheehy, his former student who is now the Collections Manager in Herpetology at the Florida Museum of Natural History, and then-Fulbright visiting scholar Jenna Crowe-Riddell.

"How these animals locate and harvest precipitation is important in view of the recent declines and extinctions of some species of sea snakes," said Lillywhite. The question remains: How will climate change and its effects on precipitation impact the sea snakes?

Journal Reference:
Harvey B. Lillywhite et al, Drinking by sea snakes from oceanic freshwater lenses at first rainfall ending seasonal drought, PLOS ONE (2019). DOI: 10.1371/journal.pone.0212099

Acquisition of fresh water (FW) is problematic for FW-dependent animals living in marine environments that are distant from sources of FW associated with land. Knowledge of how marine vertebrates respond to oceanic rainfall, and indeed the drinking responses of vertebrates generally following drought, is extremely scant. The Yellow-bellied Sea Snake (Hydrophis platurus) is the only pelagic species of squamate reptile and ranges across the Indo-Pacific oceans, having one of the largest geographic distributions of any vertebrate species. It requires FW and dehydrates at sea during periods of drought. Here we report drinking behaviors of sea snakes precisely at the transition from dry to wet season when rainfall first impacted the ocean following 6 months of seasonal drought. We show that the percentage of sea snakes that voluntarily drank FW in the laboratory when captured over eight successive days decreased from 80% to 13% before and after rainfall commenced, respectively. The percentage of snakes that drank immediately following capture exhibited a significant linear decline as the earliest rains of the wet season continued. Drinking by snakes indicates thirst related to dehydration, and thus thirsty snakes must have dehydrated during the previous six months of drought. Hence, the progressive decline in percentage of thirsty snakes indicates they were drinking from FW lenses associated with the first rainfall events of the wet season. These data reinforce the importance of accessing oceanic FW from precipitation, with implications for survival and distribution of pelagic populations that might be subjected to intensifying drought related to climate change.
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