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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).
|Sub grouping||Sea monster|
|Other name(s)||Worm, wyrm, sea dragon|
The Drachenkampf mytheme, the chief god in the role of the hero slaying a sea serpent, is widespread both in the ancient Near East and in Indo-European mythology, e.g. Lotan and Hadad, Leviathan and Yahweh, Tiamat and Marduk (see also Labbu, Bašmu, Mušḫuššu), Illuyanka and Tarhunt, Yammu and Baal in the Baal Cycle etc. The Hebrew Bible also has less mythological descriptions of large sea creatures as part of creation under God's command, such as the Tanninim mentioned in Book of Genesis 1:21 and the "great serpent" of Amos 9:3. In the Aeneid, a pair of sea serpents killed Laocoön and his sons when Laocoön argued against bringing the Trojan Horse into Troy.
In antiquity and in the Bible, dragons were envisioned as huge serpentine monsters, which means that the image of a dragon with two or four legs and wings came much later during the Late Middle Ages. Stories depicting sea-dwelling serpents may include the Babylonian myths of Tiamat, the myths of the Hydra, Scylla, Cetus, and Echidna in Greek mythology, and Christianity's Leviathan.
In Norse mythology, Jörmungandr (or Midgarðsormr) was a sea serpent so long that it encircled the entire world, Midgard. Some stories report of sailors mistaking its back for a chain of islands. Sea serpents also appear frequently in later Scandinavian folklore, particularly in that of Norway.
In 1028 AD, Saint Olaf is said to have killed a sea serpent in Valldal, Norway, throwing its body onto the mountain Syltefjellet. Marks on the mountain are associated with the legend. In Swedish ecclesiastic and writer Olaus Magnus's Carta marina, many marine monsters of varied form, including an immense sea serpent, appear. In his 1555 work History of the Northern Peoples, Magnus gives the following description of a Norwegian sea serpent:
Those who sail up along the coast of Norway to trade or to fish, all tell the remarkable story of how a serpent of fearsome size, from 200 feet [60 m] to 400 feet [120 m] long, and 20 feet [6 m] wide, resides in rifts and caves outside Bergen. On bright summer nights this serpent leaves the caves to eat calves, lambs and pigs, or it fares out to the sea and feeds on sea nettles, crabs and similar marine animals. It has ell-long hair hanging from its neck, sharp black scales and flaming red eyes. It attacks vessels, grabs and swallows people, as it lifts itself up like a column from the water.
Norwegian Bishop Erik Pontoppidan (1698–1764) is more cautious than the Archbishop of Upsala and does not believe that sea serpents would prey on ships. On the other hand, according to sailors of the time, serpents would destroy ships by wrapping the ship in coils of their body and pulling it underwater. Sailors threatened by a sea serpent were said to have thrown large objects such as paddles or shovels overboard in the path of the serpent, hoping that the serpent would take the object and leave without destroying the ship. 
An apparent eye-witness account is found in Aristotle's Historia Animalium. Strabo makes reference to an eyewitness account of a dead sea creature sighted by Poseidonius on the coast of the northern Levant. He reports the following: "As for the plains, the first, beginning at the sea, is called Macras, or Macra-Plain. Here, as reported by Poseidonius, was seen the fallen dragon, the corpse of which was about a plethrum [30 m or 100 feet] in length, and so bulky that horsemen standing by it on either side could not see one another, and its jaws were large enough to admit a man on horseback, and each flake of its horny scales exceeded an oblong shield in length." The creature was seen sometime between 130 and 51 BC.
Hans Egede, the national saint of Greenland, gives an 18th-century description of a sea serpent. On July 6, 1734, his ship sailed past the coast of Greenland when suddenly those on board "saw a most terrible creature, resembling nothing they saw before. The monster lifted its head so high that it seemed to be higher than the crow's nest on the mainmast. The head was small and the body short and wrinkled. The unknown creature was using giant fins which propelled it through the water. Later the sailors saw its tail as well. The monster was longer than our whole ship", wrote Egede.
In 1845, a 35 meter long skeleton claimed as belonging to an extinct sea serpent was put on a show in the New York City by Albert C. Koch. The claim was debunked by Prof. Jeffries Wyman, an anatomist who went to see the skeleton for himself. Wyman declared that the skull of the animal had to be mammalian in origin, and that the skeleton was composed of bones of several different animals, including an extinct species of whale.
On 6 August 1848, Captain McQuhae of HMS Daedalus and several of his officers and crew (en route to St Helena) saw a sea serpent which was subsequently reported (and debated) in The Times. The vessel sighted what they named as an enormous serpent between the Cape of Good Hope and St Helena. The serpent was witnessed to have been swimming with 1.2 m (4 feet) of its head above the water and they believed that there was another 18 m (60 feet) of the creature in the sea. Captain McQuahoe also said that "[The creature] passed rapidly, but so close under our lee quarter, that had it been a man of my acquaintance I should have easily have recognized his features with the naked eye." According to seven members of the crew, it remained in view for around twenty minutes. Another officer wrote that the creature was more of a lizard than a serpent. Evolutionary biologist Gary J. Galbreath contends that what the crew of Daedalus saw was a sei whale.
On the morning of the 31st December, 1848, in lat. 41° 13'N., and long. 12° 31'W., being nearly due west of Oporto, I saw a long black creature with a sharp head, moving slowly, I should think about two knots [3.7 km/h; 2.3 mph] ... its back was about twenty feet [6 m] if not more above water; and its head, as near as I could judge, from six to eight [1.8 to 2.4 m] ...There was something on its back that appeared like a mane, and, as it moved through the water, kept washing about; but before I could examine it more closely, it was too far astern— "A Naval Officer"
- "A giant snake appeared at once from the water - and the largest cetacean a boa constrictor way wrapped twice. (I note such a physeter It can grow to 20-30 meters long!) It lasted for about 15 minutes the deadly struggle, the sea was just foaming and crashing waves around us, finally the back of the whale stood out Out of the water, he sank head first into the deep where the snake must have killed him. A cold shiver ran through us a cet at the sight of his final struggle; so writhing poor in the monster's double ring, like a little bird between the claws of a falcon. View of the two rings, the snake. It could have been 160-170 feet long and 7-8 feet thick."
A sea serpent depicted in the coat of arms of Seljord in Norway
Sea serpent reported by Hans Egede, Bishop of Greenland, in 1734. Henry Lee suggested the giant squid as an explanation.
Albert Koch's 35-metre-long (115-foot) "Hydrarchos" fossil skeleton from 1845. It was found to be an assembled collection of bones from at least five fossil specimens of Basilosaurus.
"Supposed Appearance Of The Great Sea-Serpent, From H.M.S. Plumper, Sketched By An Officer On Board", Illustrated London News, 14 April 1849
Oarfish that washed ashore on a Bermuda beach in 1860. The animal was 5 m (16 feet) long and was originally described as a sea serpent.
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- Video of the oarfish, a creature that possibly inspired the sea serpent mythology.