Snubnosed eel
Encyclopedia
The snubnosed eel, Simenchelys parasitica, also known as the pug-nosed eel, slime eel, or snub-nose parasitic eel, is a species of deep-sea eel
and the only member of its genus. Some authors classify it as the sole member of the subfamily Simenchelyinae of the family Synaphobranchidae, or cutthroat eel
s, while others place it in its own monotypic family, the Simenchelyidae. It is found in the Atlantic and Pacific Ocean
s, typically at a depth of 500–1800 m (1,640.4–5,905.5 ft) near the bottom. Although typically a scavenger
, it is better known for using its powerful jaws and teeth to burrow into larger fishes as a parasite.
This species is harmless to humans and of no interest to fisheries. The generic name Simenchelys translates literally as "pug-nosed eel". In 2002, Koyama et al. reported that they had cultured cells from the pectoral fin of a snubnosed eel and maintained them in vitro for over a year. This represents one of the first cases of successful long-term tissue culture derived from a deep-sea multicellular organism, and has implications for a range of biotechnological
fields.
to Madeira
and the Azores
, as well as from off Cape Verde
and South Africa
. In the western Atlantic, it has been captured off the coast of the United States
. In the Pacific, it occurs off Japan
, Australia
, New Zealand
, and Hawaii
. They have been recorded from 136 to 2620 m (446.2 to 8,595.8 ft), but are usually found between 500 and 1800 m (1,640.4 and 5,905.5 ft) on the continental slope, in water temperatures of 4 –. At some locations, large numbers of snubnosed eels have been caught over a short time, indicating local abundance or schooling behavior.
The snubnosed eel has a long, stout body that is strongly compressed posterior of the vent. The head is thick and cylindrical, with a short, blunt snout. The mouth is distinctive, consisting of a tiny horizontal slit surrounded by strongly plicate lips. The jaw
s are short and strong, with the premaxillaries and maxillaries fused into a single piece. The jaws are equipped with a single row of small, rounded, close-set teeth; the vomer
ine teeth are absent. The eyes are small and round; the anterior pair of nostril
s are short tubes and the posterior pair are slit-like. The gill
openings are small and located below the pectoral fins, which are small and triangular. The dorsal
, caudal, and anal fins are merged together, the dorsal fin base originating over the tip of the pectoral fins and the anal fin originating behind the vent. The scale
s are similar in appearance to those of Anguilla and are arranged in a right-angle basketweave pattern. The coloration is gray to grayish brown, becoming darker at the fin margins and along the lateral line
. This species attains a length of 61 cm (24 in).
s (Tharybis spp.) and amphipods. Adults appear to be specialized hagfish
-like scavengers, using their powerfully muscled jaws and short, stout teeth to tear away chunks of flesh from carcasses that have fallen to the sea floor. However, this eel is more notorious for its parasitic habits, which are often repeated in literature. Frank Thomas Bullen
, in the 1904 Denizens of the Deep, wrote that the eel "attaches himself to the bodies of the larger, fleshier fish, such as halibut
, and by sheer force of suction and boring withal works his ravenous way right into their bodies, at what misery to his involuntary hosts can only be imagined." Spencer Fullerton Baird
reported that the eels are "not unfrequently found nestling along the backbone
of the halibut and cod
, where they seem to have the power of abiding for some time without actually causing death." Baird also made note of the eels' supposed habit of burrowing into the abdominal cavities of netted, gravid shad
and eating their eggs within the span of "a few minutes".
In 1992, two snubnose eels were discovered inside the heart
of a 395 kg (870.8 lb) shortfin mako shark
(Isurus oxyrhinchus) landed at Montauk, New York
. The two eels, both immature females, measured 21 and 24 cm (8.3 and 9.4 in) long and had fed on blood
, with histiological evidence suggesting that they had been there long enough for arteriosclerosis
and hyperplasia
(indicative of circulatory obstruction or toxicity from metabolic wastes), and tissue regeneration to occur. The authors speculated that the eels had burrowed into the shark through the gills or throat (the precise path of entry could not be determined, possibly obscured by damage caused by the tow rope) after it had been weakened on the capture line, entered the circulatory system
, and then made their way to the heart. Despite records of its parasitic behavior, submersible
encounters with free-swimming juveniles and adults, and their capture in baited traps, suggest that this species is at most a facultative parasite that opportunistically enters sick and dying fish.
Reproduction is oviparous. The eggs
are likely pelagic, measuring at least 2 mm (0.078740157480315 in) across, and lack an oil globule. An ovary
from one 51 cm (20.1 in) female examined contained about 30,000 eggs. Like all other eels, the snubnosed eel undergoes a leptocephalus
larva
l stage that metamorphoses
into a juvenile form resembling the adult. Leptocephali belonging to this species have yet to be identified, but based on the appearance of the metamorphic stage, they likely have long bodies with short heads and small mouths, and little to no body pigmentation. Metamorphic fish are white, with the black peritoneum
clearly visible; one known metamorphic specimen measured 11 cm (4.3 in) long. Sexual maturation is attained at around a length of 50–53 cm (19.7–20.9 in). The trematode Hypertrema ambovatum is a known parasite of this species, infesting the intestines.
Eel
Eels are an order of fish, which consists of four suborders, 20 families, 111 genera and approximately 800 species. Most eels are predators...
and the only member of its genus. Some authors classify it as the sole member of the subfamily Simenchelyinae of the family Synaphobranchidae, or cutthroat eel
Cutthroat eel
Cutthroat eels are a family, Synaphobranchidae, of eels, the only member of the suborder Synaphobranchoidei. They are found worldwide in temperate and tropical seas....
s, while others place it in its own monotypic family, the Simenchelyidae. It is found in the Atlantic and Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
s, typically at a depth of 500–1800 m (1,640.4–5,905.5 ft) near the bottom. Although typically a scavenger
Scavenger
Scavenging is both a carnivorous and herbivorous feeding behavior in which individual scavengers search out dead animal and dead plant biomass on which to feed. The eating of carrion from the same species is referred to as cannibalism. Scavengers play an important role in the ecosystem by...
, it is better known for using its powerful jaws and teeth to burrow into larger fishes as a parasite.
This species is harmless to humans and of no interest to fisheries. The generic name Simenchelys translates literally as "pug-nosed eel". In 2002, Koyama et al. reported that they had cultured cells from the pectoral fin of a snubnosed eel and maintained them in vitro for over a year. This represents one of the first cases of successful long-term tissue culture derived from a deep-sea multicellular organism, and has implications for a range of biotechnological
Biotechnology
Biotechnology is a field of applied biology that involves the use of living organisms and bioprocesses in engineering, technology, medicine and other fields requiring bioproducts. Biotechnology also utilizes these products for manufacturing purpose...
fields.
Distribution and habitat
In the eastern Atlantic, the snubnosed eel is known from FranceFrance
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
to Madeira
Madeira
Madeira is a Portuguese archipelago that lies between and , just under 400 km north of Tenerife, Canary Islands, in the north Atlantic Ocean and an outermost region of the European Union...
and the Azores
Azores
The Archipelago of the Azores is composed of nine volcanic islands situated in the middle of the North Atlantic Ocean, and is located about west from Lisbon and about east from the east coast of North America. The islands, and their economic exclusion zone, form the Autonomous Region of the...
, as well as from off Cape Verde
Cape Verde
The Republic of Cape Verde is an island country, spanning an archipelago of 10 islands located in the central Atlantic Ocean, 570 kilometres off the coast of Western Africa...
and South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
. In the western Atlantic, it has been captured off the coast of the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. In the Pacific, it occurs off Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, and Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
. They have been recorded from 136 to 2620 m (446.2 to 8,595.8 ft), but are usually found between 500 and 1800 m (1,640.4 and 5,905.5 ft) on the continental slope, in water temperatures of 4 –. At some locations, large numbers of snubnosed eels have been caught over a short time, indicating local abundance or schooling behavior.
Description
Jaw
The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of...
s are short and strong, with the premaxillaries and maxillaries fused into a single piece. The jaws are equipped with a single row of small, rounded, close-set teeth; the vomer
Vomer
The vomer is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones.-Biology:...
ine teeth are absent. The eyes are small and round; the anterior pair of nostril
Nostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
s are short tubes and the posterior pair are slit-like. The gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
openings are small and located below the pectoral fins, which are small and triangular. The dorsal
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
, caudal, and anal fins are merged together, the dorsal fin base originating over the tip of the pectoral fins and the anal fin originating behind the vent. The scale
Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...
s are similar in appearance to those of Anguilla and are arranged in a right-angle basketweave pattern. The coloration is gray to grayish brown, becoming darker at the fin margins and along the lateral line
Lateral line
The lateral line is a sense organ in aquatic organisms , used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail...
. This species attains a length of 61 cm (24 in).
Biology and ecology
Early juvenile snubnosed eels feed on epibenthic copepodCopepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
s (Tharybis spp.) and amphipods. Adults appear to be specialized hagfish
Hagfish
Hagfish, the clade Myxini , are eel-shaped slime-producing marine animals . They are the only living animals that have a skull but not a vertebral column. Along with lampreys, hagfish are jawless and are living fossils whose next nearest relatives include all vertebrates...
-like scavengers, using their powerfully muscled jaws and short, stout teeth to tear away chunks of flesh from carcasses that have fallen to the sea floor. However, this eel is more notorious for its parasitic habits, which are often repeated in literature. Frank Thomas Bullen
Frank Thomas Bullen
Frank Thomas Bullen , British author and novelist, was born of poor parents in Paddington, London, on 5 April 1857, and was educated for a few years at a dame school and Westbourne school, Paddington. At the age of 9 he left school and took up work as an errand boy. In 1869 he went to sea and...
, in the 1904 Denizens of the Deep, wrote that the eel "attaches himself to the bodies of the larger, fleshier fish, such as halibut
Halibut
Halibut is a flatfish, genus Hippoglossus, from the family of the right-eye flounders . Other flatfish are also called halibut. The name is derived from haly and butt , for its popularity on Catholic holy days...
, and by sheer force of suction and boring withal works his ravenous way right into their bodies, at what misery to his involuntary hosts can only be imagined." Spencer Fullerton Baird
Spencer Fullerton Baird
Spencer Fullerton Baird was an American ornithologist, ichthyologist and herpetologist. Starting in 1850 he was assistant-secretary and later secretary of the Smithsonian Institution in Washington, D.C...
reported that the eels are "not unfrequently found nestling along the backbone
Backbone
Backbone may refer to:* Vertebral column, of a vertebrate organism* Backbone chain, in polymer chemistry, the framework of the molecule* Backbone Entertainment, a video game development company* Backbone network, the top level of a hierarchical network...
of the halibut and cod
Cod
Cod is the common name for genus Gadus, belonging to the family Gadidae, and is also used in the common name for various other fishes. Cod is a popular food with a mild flavor, low fat content and a dense, flaky white flesh. Cod livers are processed to make cod liver oil, an important source of...
, where they seem to have the power of abiding for some time without actually causing death." Baird also made note of the eels' supposed habit of burrowing into the abdominal cavities of netted, gravid shad
Shad
The shads or river herrings comprise the genus Alosa, fish related to herring in the family Clupeidae. They are distinct from others in that family by having a deeper body and spawning in rivers. The several species frequent different areas on both sides of the Atlantic Ocean, Mediterranean Sea....
and eating their eggs within the span of "a few minutes".
In 1992, two snubnose eels were discovered inside the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
of a 395 kg (870.8 lb) shortfin mako shark
Shortfin mako shark
The shortfin mako shark, Isurus oxyrinchus , is a large mackerel shark. Along with the closely related longfin mako it is commonly referred to as a "mako shark".-Etymology:...
(Isurus oxyrhinchus) landed at Montauk, New York
Montauk, New York
Montauk [ˈmɒntɒk] is a census-designated place that roughly corresponds to the hamlet with the same name located in the town of East Hampton in Suffolk County, New York, United States on the South Shore of Long Island. As of the United States 2000 Census, the CDP population was 3,851 as of 2000...
. The two eels, both immature females, measured 21 and 24 cm (8.3 and 9.4 in) long and had fed on blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
, with histiological evidence suggesting that they had been there long enough for arteriosclerosis
Arteriosclerosis
Arteriosclerosis refers to a stiffening of arteries.Arteriosclerosis is a general term describing any hardening of medium or large arteries It should not be confused with "arteriolosclerosis" or "atherosclerosis".Also known by the name "myoconditis" which is...
and hyperplasia
Hyperplasia
Hyperplasia means increase in number of cells/proliferation of cells. It may result in the gross enlargement of an organ and the term is sometimes mixed with benign neoplasia/ benign tumor....
(indicative of circulatory obstruction or toxicity from metabolic wastes), and tissue regeneration to occur. The authors speculated that the eels had burrowed into the shark through the gills or throat (the precise path of entry could not be determined, possibly obscured by damage caused by the tow rope) after it had been weakened on the capture line, entered the circulatory system
Circulatory system
The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...
, and then made their way to the heart. Despite records of its parasitic behavior, submersible
Submersible
A submersible is a small vehicle designed to operate underwater. The term submersible is often used to differentiate from other underwater vehicles known as submarines, in that a submarine is a fully autonomous craft, capable of renewing its own power and breathing air, whereas a submersible is...
encounters with free-swimming juveniles and adults, and their capture in baited traps, suggest that this species is at most a facultative parasite that opportunistically enters sick and dying fish.
Reproduction is oviparous. The eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
are likely pelagic, measuring at least 2 mm (0.078740157480315 in) across, and lack an oil globule. An ovary
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
from one 51 cm (20.1 in) female examined contained about 30,000 eggs. Like all other eels, the snubnosed eel undergoes a leptocephalus
Leptocephalus
A leptocephalus is the flat and transparent larva of the eel, marine eels, and other members of the Superorder Elopomorpha. Fishes with a leptocephalus larva stage include the most familiar eels such as the conger, moray eel, and garden eel, and the freshwater eels of the family Anguillidae, plus...
larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
l stage that metamorphoses
Metamorphosis
Metamorphosis is a biological process by which an animal physically develops after birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation...
into a juvenile form resembling the adult. Leptocephali belonging to this species have yet to be identified, but based on the appearance of the metamorphic stage, they likely have long bodies with short heads and small mouths, and little to no body pigmentation. Metamorphic fish are white, with the black peritoneum
Peritoneum
The peritoneum is the serous membrane that forms the lining of the abdominal cavity or the coelom — it covers most of the intra-abdominal organs — in amniotes and some invertebrates...
clearly visible; one known metamorphic specimen measured 11 cm (4.3 in) long. Sexual maturation is attained at around a length of 50–53 cm (19.7–20.9 in). The trematode Hypertrema ambovatum is a known parasite of this species, infesting the intestines.