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

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.

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.[1]

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 bacause 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.[2]

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.[3]

In 1766, Linnaeus referred to the yellow-bellied sea snake as 'Anguis patura' (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.[4] 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.[5]

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.[6].

Though highly venomous, Pelamis platurus is less venomous 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. "[7] 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[8]. The venomousness of Pelamis platurus is: Mouse LD50 (mg/kg) : 0.07 Venom yield per snake (mg) : 1.0-4.0 [9] Below is the comparative venomousness of the other snakes mentioned:

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.[11] [12] The (Enhydrina schistosa) antivenom was tested specifically on Pelamus platurus and it effectively neutralised the venom.[13]