The snailfishes or sea snails (not to be confused with invertebrate sea snails), are a

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

of marine

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of sk ...

es. These fishes make up the Liparidae, a family classified within the

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

Scorpaeniformes. Widely distributed from the

Arctic The Arctic (; . ) is the polar regions of Earth, polar region of Earth that surrounds the North Pole, lying within the Arctic Circle. The Arctic region, from the IERS Reference Meridian travelling east, consists of parts of northern Norway ( ...

Antarctic Ocean The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the world ocean, generally taken to be south of 60th parallel south, 60° S latitude and encircling Antarctica. With a size of , it is the seco ...

s, including the oceans in between, the snailfish family contains more than 30 genera and about 410 described species, but there are also many

undescribed species In taxonomy, an undescribed taxon is a taxon (for example, a species) that has been discovered, but not yet formally described and named. The various Nomenclature Codes specify the requirements for a new taxon to be validly described and named. U ...

. Snailfish are found at depths ranging from shallow coastal waters to more than , including in seven ocean trenches.

Taxonomy

The snailfish family, Liparidae, was first proposed by the American biologist Theodore Gill in 1861. The 5th edition of ''

Fishes of the World ''Fishes of the World'' is a standard reference for the systematics of fishes. It was first written in 1976 by the American ichthyologist Joseph S. Nelson (1937–2011). Now in its fifth edition (2016), the work is a comprehensive overview of t ...

'' classifies this family within superfamily Cyclopteroidea, part of the

suborder Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and recognized ...

Cottoidei Cottoidei is a suborder of ray-finned fishes which, according to the 5th edition of ''Fishes of the World'', is placed within the order Scorpaeniformes, alongside the scorpionfishes, flatheads, eelpouts, sticklebacks and related fishes. Taxon ...

of the order

Scorpaeniformes The Scorpaeniformes are a diverse Order (biology), order of Actinopterygii, ray-finned fish, including the lionfishes and sculpins, but have also been called the Scleroparei. It is one of the five largest orders of bony fishes by number of spec ...

. Other authorities do not recognise this superfamily and classify the two families within it, Cyclopteridae and Liparidae, within the

infraorder Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between Family_(biology), family and Class_(biology), class. In biological classification, the order is a taxonomic rank used in the classific ...

Cottales alongside the sculpins, within the order

Perciformes Perciformes (), also called the Acanthopteri, is an order or superorder of ray-finned fish in the clade Percomorpha. ''Perciformes'' means " perch-like". Among the well-known members of this group are perches and darters ( Percidae), and als ...

. An osteological analysis found that the genus '' Bathylutichthys'' was intermediate between the Psychrolutidae and the two families making up the Cyclopteroidea, meaning that those two families would not be supported as a superfamily within the

Molecular biology

Species of deep-sea snailfish have been studied and compared to other

es (also known as teleosts) to analyze their adaptions to deep-sea conditions. The genomes of both the Yap hadal snailfish and Mariana hadal snailfish have been found to contain an abundance of the ''fmo3'' gene, which produces the trimethylamine ''N''-oxide (TMAO) protein stabilizer. Analysis of Yap hadal snailfish reveals a loss of olfactory receptors and gain of taste receptors, possibly due to the fairly restricted availability of food in the deep-sea. Additionally, perhaps due to lack of light in the deep sea, the Yap genome includes fewer copies of

crystallin In anatomy, a crystallin is a water-soluble structural protein found in the lens and the cornea of the eye accounting for the transparency of the structure. It has also been identified in other places such as the heart, and in aggressive breast ...

genes, which encode proteins that sense light and assist in focused vision, in comparison to other teleosts. Meanwhile, Mariana hadal snailfish have lost several photoreceptor genes, decreasing their vision capabilities (especially in terms of color), and have completely lost the '' mc1r'' pigmentation gene, rendering them colorless. Mariana hadal snailfish also have adjusted to pressure due to a mutation in ''bglap'' which prevents cartilage calcification, revealed in their skulls. Further, their genome includes increased amounts of genes encoding enzymes for beta oxidation and transport proteins, thereby increasing membrane fluidity.

Description

Snailfish have an elongated,

tadpole A tadpole or polliwog (also spelled pollywog) is the Larva, larval stage in the biological life cycle of an amphibian. Most tadpoles are fully Aquatic animal, aquatic, though some species of amphibians have tadpoles that are terrestrial animal, ...

-like shape. Their heads are large in comparison to their body and they have small eyes. Their bodies are slender but deep and they taper to very small tails. The extensive dorsal and anal

fins A fin is a thin component or appendage attached to a larger body or structure. Fins typically function as foil (fluid mechanics), foils that produce lift (force), lift or thrust, or provide the ability to steer or stabilize motion while travelin ...

may merge or nearly merge with the tail fin. Snailfish are scaleless with a thin, loose

gelatin Gelatin or gelatine () is a translucent, colorless, flavorless food ingredient, commonly derived from collagen taken from animal body parts. It is brittle when dry and rubbery when moist. It may also be referred to as hydrolyzed collagen, coll ...

ous skin which surrounds the spine and can vary in terms of size and shape between species. The gelatinous layer has a high water and low protein, lipid and carbohydrate content, therefore it can provide growth with low metabolic cost. This may aid species in avoiding predation and conserving energy, especially for deep sea snailfish who live in low energy conditions. Some species, such as '' Acantholiparis opercularis'', have prickly spines as well. Their teeth are small and simple with blunt cusps. The deep-sea species have prominent, well-developed sensory pores on the head, part of the animals'

lateral line The lateral line, also called the lateral line organ (LLO), is a system of sensory organs found in fish, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory ability is achieved via modified epithelia ...

system. The pectoral fins are large and provide the snailfish with its primary means of locomotion, although they are fragile. In some species such as the antarctic ''Paraliparis devries''i, the pectoral fins have an expanded somatosensory system, including a taste bud. The snailfish are

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...

fish with pelvic fins modified to form an adhesive disc; this nearly circular disc is absent in '' Paraliparis'' and '' Nectoliparis'' species. Research has revealed that maximum depth of living can be a significant predictor for loss of the pelvic disk in certain species of snailfish. Based on phylogenetic analysis, this ancestral feature has been lost three separate times in Snailfish. Snailfish range in size from ''Paraliparis australis'' at to '' Polypera simushirae'' at some in length. The latter species may reach a weight of , but most species are smaller. Snailfish are of no interest to commercial

fisheries Fishery can mean either the enterprise of raising or harvesting fish and other aquatic life or, more commonly, the site where such enterprise takes place ( a.k.a., fishing grounds). Commercial fisheries include wild fisheries and fish farm ...

. The deepest snailfish do not explode when brought to the surface, because they do not have a swim bladder. However, they do not survive capture, possibly due to molecular effects of depressurization. Many intact specimens have been retrieved in recent years for biochemical and anatomical study. Buoyancy without a swimbladder is due to gelatinous tissue and low-calcium bones ef. 10

Occurrence and habitat

Snailfish habitats vary widely. They are found in oceans worldwide, ranging from shallow intertidal zones to depths of more than in the

hadal zone The hadal zone, also known as the hadopelagic zone, is the deep sea, deepest region of the ocean, lying within oceanic trenches. The hadal zone ranges from around below sea level, and exists in long, narrow, topographic V-shaped depressions. T ...

. This is a wider depth range than any other family of fish. They are strictly found in cold waters, meaning that species of tropical and

subtropical The subtropical zones or subtropics are geographical zone, geographical and Köppen climate classification, climate zones immediately to the Northern Hemisphere, north and Southern Hemisphere, south of the tropics. Geographically part of the Ge ...

regions strictly are deepwater. They are common in most cold marine waters and are highly resilient, with some species, such as '' Liparis atlanticus'' and '' Liparus gibbus,'' having type-1

antifreeze protein Antifreeze proteins (AFPs) or ice structuring proteins refer to a class of polypeptides produced by certain animals, plants, fungi and bacteria that permit their survival in temperatures below the freezing point of water. AFPs bind to small ...

s. It is the most species-rich family of fish in the Antarctic region, generally found in relatively deep waters (shallower Antarctic waters are dominated by Antarctic icefish). The diminutive inquiline snailfish (''Liparis inquilinus'') of the northwestern Atlantic is known to live out its life inside the mantle cavity of the scallop '' Placopecten magellanicus''. '' Liparis tunicatus'' lives amongst the

kelp forest Kelp forests are underwater areas with a high density of kelp, which covers a large part of the world's coastlines. Smaller areas of anchored kelp are called kelp beds. They are recognized as one of the most productive and dynamic ecosystems on E ...

s of the

Bering Strait The Bering Strait ( , ; ) is a strait between the Pacific and Arctic oceans, separating the Chukchi Peninsula of the Russian Far East from the Seward Peninsula of Alaska. The present Russia–United States maritime boundary is at 168° 58' ...

and the Gulf of St. Lawrence. The single species in genus ''Rhodichthys'' is endemic to the

Norwegian Sea The Norwegian Sea (; ; ) is a marginal sea, grouped with either the Atlantic Ocean or the Arctic Ocean, northwest of Norway between the North Sea and the Greenland Sea, adjoining the Barents Sea to the northeast. In the southwest, it is separate ...

. Other species are found on muddy or silty bottoms of

continental slope A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental margi ...

Depth record

Although most snailfish live no deeper than the

bathyal zone The bathypelagic zone or bathyal zone (from Greek βαθύς (bathýs), deep) is the part of the open ocean that extends from a depth of below the ocean surface. It lies between the mesopelagic above and the abyssopelagic below. The bathypela ...

(less than deep), some live at greater depths than any other fish. In 2008, a UK-Japan team discovered a

shoal In oceanography, geomorphology, and Earth science, geoscience, a shoal is a natural submerged ridge, bank (geography), bank, or bar that consists of, or is covered by, sand or other unconsolidated material, and rises from the bed of a body ...

of '' Pseudoliparis amblystomopsis'' snailfish at a depth of in the Japan Trench. These were, at the time, the deepest living fish ever recorded on film. The record was surpassed by snailfish filmed in the

Mariana Trench The Mariana Trench is an oceanic trench located in the western Pacific Ocean, about east of the Mariana Islands; it is the deep sea, deepest oceanic trench on Earth. It is crescent-shaped and measures about in length and in width. The maxi ...

at depths of in 2014 and in 2017, and at in the Izu–Ogasawara Trench in 2023. The species in these deepest records are unknown and may be undescribed, but have been referred to as "ethereal snailfish". The deepest-living described species is '' Pseudoliparis swirei'', of the Mariana Trench, recorded at . Snailfish (notably genera '' Notoliparis'' and '' Pseudoliparis'') are the most common and dominant fish family in the

. '' Pseudoliparis swirei'' possesses multiple molecular adaptations to the intense pressures of a deep sea environment, including highest-known contents of TMAO efs. 14, 24 pressure-tolerant

cartilage Cartilage is a resilient and smooth type of connective tissue. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints ...

, pressure-stable proteins, increased transport protein activity, higher cell membrane fluidity, and loss of eyesight and other visual characteristics such as color, as shown by genomic analysis. Because of

biochemical Biochemistry, or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology, ...

restrictions, is likely the maximum depth possible for any vertebrate. The

larvae A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect developmental biology, development such as insects, some arachnids, amphibians, or cnidarians typical ...

of some hadal snailfish species may spend time in open water at relatively shallow depths, less than .

Reproduction and life span

Reproductive strategies vary extensively among snailfish species, though it is thought that many abyssal benthic snailfish spawn seasonally and for relatively long intervals. It appears that all species lay relatively large eggs (diameter up to ) and the number of eggs is species dependent. The larger size of eggs in hadal snailfish species indicates continuous spawning. Some species deposit their egg masses among cold-water corals,

kelp Kelps are large brown algae or seaweeds that make up the order (biology), order Laminariales. There are about 30 different genus, genera. Despite its appearance and use of photosynthesis in chloroplasts, kelp is technically not a plant but a str ...

, stones, or

xenophyophores Xenophyophorea is a clade of foraminiferans. Xenophyophores are multinucleate unicellular organisms found on the ocean floor throughout the world's oceans, at depths of . They are a kind of foraminiferan that extract minerals from their surround ...

and males will sometimes guard the egg mass. At least one species, ''Careproctus ovigerus'' of the North Pacific, practices mouth brooding where the male snailfish carries the developing eggs around in his mouth. Some other species of the genus '' Careproctus,'' are

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...

, laying their eggs in the gill cavities of king crabs. The eggs put pressure on the crabs' gills which can cause the gill tissue to be damaged or die altogether. However, the survival of snailfish larvae has been shown to increase by the snailfish utilizing the crab host species as a way to care for and aerate their eggs. The eggs themselves are self-adhesive and tend to form masses that replicate the shape of the internal branchial chambers of crabs. Additionally, at least one species of snailfish that utilize the golden king crab as a host, ''Careproctus pallidus,'' has larvae with a lower energy content than normal for most marine fish. A possible explanation for starting life with less energy is due to the safety provided by the king crab, allowing the adult snailfish to not expend as much energy producing an energy-rich yolk sac. A different species, ''Careproctus rhodomelas'', was found to be a batch spawner, laying multiple batches of large eggs multiple times throughout its lifetime. After the eggs hatch, some species rapidly reach the adult size and only live for about one year, but others live for more than a decade.

Otolith An otolith (, ' ear + , ', a stone), also called otoconium, statolith, or statoconium, is a calcium carbonate structure in the saccule or utricle (ear), utricle of the inner ear, specifically in the vestibular system of vertebrates. The saccule ...

analysis (the investigation of snailfish ear bone) gives insight into longevity by seeing how it is broken into alternating translucent and opaque zones. This relays information about annual growth. By further examining the morphology of the deep-sea snailfish, it may be evident that these snailfish have adapted to their extreme environment by having a short life span compared to other organisms in the same hadal environment. Many species are located in hadal trenches, which are inherently high-disturbance areas, including lots of seismic activity which can trigger turbidity flows. Because of this, they live significantly shorter lifespans than shallower species. Little is known about snailfish courtship behavior but males of ''Careproctus pallidus'' are believed to wiggle their bodies as attractive or aggressive display. It is thought that in an environment so dark, it is hard to find and win contests for a mate. Therefore, snailfish use hydrodynamic signals that are felt by the mechanosensory

to communicate.

Diet

Larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

l snailfish feed on a mix of

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

, small and large

copepod Copepods (; meaning 'oar-feet') are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (living in the water column), some are benthos, benthic (living on the sedimen ...

s, and

amphipods Amphipoda () is an order (biology), order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods () range in size from and are mostly detritivores or scavengers. There are more than 10,700 amphip ...

. The larval diet of three

Beaufort Sea The Beaufort Sea ( ; ) is a marginal sea of the Arctic Ocean, located north of the Northwest Territories, Yukon, and Alaska, and west of the Canadian Arctic Archipelago. The sea is named after Sir Francis Beaufort, a Hydrography, hydrographer. T ...

snailfish species contained 28 food categories, mainly copepods and amphipods. Snailfish prey fall into six main categories: gammarid,

krill Krill ''(Euphausiids)'' (: krill) are small and exclusively marine crustaceans of the order (biology), order Euphausiacea, found in all of the world's oceans. The name "krill" comes from the Norwegian language, Norwegian word ', meaning "small ...

, natantian decapods, other crustaceans, fish, and others. Size also affects snailfish diets; snailfish smaller than 50 mm primarily eat gammarids, while species larger than 100 mm primarily eat natantian decapods. Species larger than 150 mm have the highest proportion of fish in their diet. The largest snailfish species tend to be

piscivorous A piscivore () is a carnivorous animal that primarily eats fish. Fish were the diet of early tetrapod evolution (via water-bound amphibians during the Devonian period); insectivory came next; then in time, the more terrestrially adapted rept ...

. With the Okhotsk snailfish (''Liparis ochotensis''), the ratio between food intake and body weight changes as the organism grows; it is also highly seasonally variable. When the local environment experiences an increase in shrimp and

crangonidae Crangonidae is a family of shrimp, of the superfamily Crangonoidea, including the commercially important species ''Crangon crangon''. Its type genus is '' Crangon''. Crangonid shrimps' first pair of pereiopods have partially chelate claws tha ...

numbers, there is also a subsequent decrease in decapods. There are also snailfish localized to the Terpeniya Bay that purely eat zooplankton, setting them apart from other snailfish. The snailfish that live in the northern hemisphere also display a higher starvation tolerance, which may be due to the triglycerol and cholesterol levels in this species. The snailfish have different lipid concentrations depending on their habitat, making some of them better-suited for longer periods without feeding than others. The ambush hunting methods employed by the Simushir snailfish (''Polypera simushirae'') are unique among snailfish. They have the ability to blend into the ground, waiting to surprise the next organism to wander into their path. The top prey for this species are fish, making up 97.7% of their overall food intake.

Genera

This family contains these genera as of 2020: * '' Acantholiparis'' Gilbert &

Burke Burke (; ) is a Normans in Ireland, Norman-Irish surname, deriving from the ancient Anglo-Norman and Hiberno-Norman noble dynasty, the House of Burgh. In Ireland, the descendants of William de Burgh (''circa'' 1160–1206) had the surname'' de B ...

, 1912 * '' Aetheliparis'' Stein, 2012 * '' Allocareproctus'' Pitruk & Fedorov, 1993 * '' Careproctus'' Krøyer, 1862 * '' Crystallias'' Jordan & Snyder, 1902 * '' Crystallichthys''

Jordan Jordan, officially the Hashemite Kingdom of Jordan, is a country in the Southern Levant region of West Asia. Jordan is bordered by Syria to the north, Iraq to the east, Saudi Arabia to the south, and Israel and the occupied Palestinian ter ...

& Gilbert, 1898 * '' Eknomoliparis'' Stein, Meléndez C. & Kong U., 1991 * '' Elassodiscus'' Gilbert & Burke, 1912 * '' Eutelichthys'' Tortonese, 1959 * '' Genioliparis'' Andriashev & Neyelov, 1976 * '' Gyrinichthys'' Gilbert, 1896 * '' Liparis'' Scopoli, 1777 * '' Lipariscus'' Gilbert, 1915 * '' Lopholiparis'' Orr, 2004 * '' Menziesichthys'' Nalbant & Mayer, 1971 * '' Nectoliparis'' Gilbert & Burke, 1912 * '' Notoliparis'' Andriashev, 1975 * '' Osteodiscus'' Stein, 1978 * '' Palmoliparis'' Balushkin, 1996 * '' Paraliparis'' Collett, 1879 * '' Polypera'' Burke, 1912 * '' Praematoliparis'' Andriashev, 2003 * '' Prognatholiparis'' Orr & Busby, 2001 * '' Psednos'' Barnard, 1927 * '' Pseudoliparis'' Andriashev, 1955 * '' Pseudonotoliparis'' Pitruk, 1991 * '' Rhinoliparis'' Gilbert, 1896 * '' Rhodichthys'' Collett, 1879 * '' Squaloliparis'' Pitruk & Fedorov, 1993 * '' Temnocora'' Burke, 1930 * '' Volodichthys'' Balushkin, 2012 Image:Acantholiparis opercularis.jpg, '' Acantholiparis opercularis'' Image:Careproctus ovigerum (juvenile).jpg, '' Careproctus ovigerus'' (juvenile) Image:Crystallichthys cyclospilus.jpg, '' Crystallichthys cyclospilus'' Image:Elassodiscus tremebundus.jpg, '' Elassodiscus tremebundus'' Image:GelatinousSeasnail.jpg, '' Liparis fabricii'' Image:Nectoliparis pelagicus.jpg, '' Nectoliparis pelagicus'' Image:Paraliparis bathybius1.jpg, '' Paraliparis bathybius'' Image:Rhodichthys regina1.jpg, '' Rhodichthys regina'' Image:Temnocora candida.jpg, '' Temnocora candida''

References

External links

* {{Authority control Liparidae Cyclopteroidea Taxa named by Theodore Gill