The viper dogfish or viper shark (''Trigonognathus kabeyai'') is a rare

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

dogfish shark Squalidae, more commonly known as dogfish, dog sharks, or spiny dogfish, are one of several families of sharks categorized under Squaliformes, making it the second largest order of sharks, numbering 119 species across 7 families. Having earned t ...

in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Etmopteridae The Etmopteridae are a family of sharks in the order Squaliformes, commonly known as lantern sharks. Their name comes from the presence of light-producing photophore A photophore is a glandular organ that appears as luminous spots on vario ...

, and the only extant member of its

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

. It has been found in the Pacific Ocean off southern Japan, the

Bonin Islands The Bonin Islands, also known as the , are an archipelago of over 30 subtropical and tropical islands, some directly south of Tokyo, Japan and northwest of Guam. The name "Bonin Islands" comes from the Japanese word ''bunin'' (an archaic readi ...

, Pacific Ocean off northern

Taitung County Taitung County (; Mandarin pinyin: ''Táidōng Xiàn''; Hokkien POJ: ''Tâi-tang-koān''; Hakka PFS: ''Thòi-tûng-yen''; Paiwan: ''Valangaw'';lit:Eastern part of Taiwan) is the third largest county in Taiwan, located primarily on the island' ...

and the

Northwestern Hawaiian Islands The Northwestern Hawaiian Islands or Leeward Hawaiian Islands are a series of islands and atolls in the Hawaiian island chain located northwest (in some cases, far to the northwest) of the islands of Kauai and Niihau. Politically, they are all p ...

. This species inhabits upper

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 margin ...

s and

seamount A seamount is a large geologic landform that rises from the ocean floor that does not reach to the water's surface (sea level), and thus is not an island, islet or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abru ...

s. It may migrate vertically, shifting between bottom waters deep during the day and upper waters less than deep at night. A slender, black shark reaching in length, the viper dogfish can be recognized by its narrow, triangular jaws and well-spaced, fang-like teeth. It also has two spined

dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through conv ...

dermal denticle A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scales, which can also provide effective camouflage through the use of reflection and colouration, as we ...

s with faceted crowns, and numerous light-emitting

photophore A photophore is a glandular organ that appears as luminous spots on various marine animals, including fish and cephalopods. The organ can be simple, or as complex as the human eye; equipped with lenses, shutters, color filters and reflectors, ...

s concentrated on its ventral surface. Feeding mainly on

bony fish Osteichthyes (), popularly referred to as the bony fish, is a diverse superclass of fish that have skeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes, which have skeletons primarily composed of cartilag ...

es, the viper dogfish captures prey by protruding its jaws and impaling them with its teeth. Its impressive gape allows it to swallow relatively large fish whole. The

skeletal A skeleton is the structural frame that supports the body of an animal. There are several types of skeletons, including the exoskeleton, which is the stable outer shell of an organism, the endoskeleton, which forms the support structure inside ...

and

muscular Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscle ...

structure of its head shows unique features that support this feeding mechanism, which is unlike that of other dogfish sharks. This shark gives birth to live young, which are nourished by

yolk Among animals which produce eggs, the yolk (; also known as the vitellus) is the nutrient-bearing portion of the egg whose primary function is to supply food for the development of the embryo. Some types of egg contain no yolk, for example bec ...

during

gestation Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pregna ...

; the litter size is probably fewer than 26 pups. Small numbers of viper dogfish are caught incidentally in

purse seine Seine fishing (or seine-haul fishing; ) is a method of fishing that employs a surrounding net, called a seine, that hangs vertically in the water with its bottom edge held down by weights and its top edge buoyed by floats. Seine nets can be dep ...

s and

bottom trawl Bottom trawling is trawling (towing a trawl, which is a fishing net) along the seafloor. It is also referred to as "dragging". The scientific community divides bottom trawling into benthic trawling and demersal trawling. Benthic trawling is towing ...

Taxonomy

The first specimens of the viper dogfish were two immature males caught off southern Japan by the

er ''Seiryo-Maru'' in 1986. The first, designated as the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

, measured long and was collected off

Cape Shiono A cape is a clothing accessory or a sleeveless outer garment which drapes the wearer's back, arms, and chest, and connects at the neck. History Capes were common in medieval Europe, especially when combined with a hood in the chaperon. Th ...

at a depth of . The second measured long and was collected off

Hiwasa, Tokushima was a town located in Kaifu District, Tokushima Prefecture, Japan. As of 2003, the town had an estimated population of 5,563 and a density Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The s ...

at a depth of . The shark was described as a new species and genus by

University of Tokyo , abbreviated as or UTokyo, is a public research university located in Bunkyō, Tokyo, Japan. Established in 1877, the university was the first Imperial University and is currently a Top Type university of the Top Global University Project by ...

researchers Kenji Mochizuki and Fumio Ohe in a 1990 article for the ''Japanese Journal of Ichthyology''. They gave it the name ''Trigonognathus kabeyai''; the generic name is derived from the

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

''trigonon'' ("triangle") and ''gnathus'' ("jaw"), while the specific name honors Hiromichi Kabeya, the captain of the ''Seiryo-Maru''. Mochizuki and Ohe originally assigned the viper dogfish to the family

Squalidae Squalidae, more commonly known as dogfish, dog sharks, or spiny dogfish, are one of several families of sharks categorized under Squaliformes, making it the second largest order of sharks, numbering 119 species across 7 families. Having earned t ...

, which at the time was used for all members of the

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

Squaliformes The Squaliformes are an order (biology), order of sharks that includes about 126 species in seven families. Members of the order have two dorsal fins, which usually possess spines, they usually have a sharp head, no anal fin or nictitating me ...

aside from the

bramble A bramble is any rough, tangled, prickly shrub, usually in the genus ''Rubus'', which grows blackberries, raspberries, or dewberries. "Bramble" is also used to describe other prickly shrubs, such as roses (''Rosa'' species). The fruits inclu ...

and rough sharks. In a 1992 morphological study, Shigeru Shirai and Osamu Okamura placed this species in the squalid subfamily Etmopterinae, which most taxonomists now recognize as the separate family Etmopteridae.

Phylogeny and evolution

The position of ''Trigonognathus'' within the Etmopteridae is uncertain. Morphological and

molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

data generally support the subdivision of the Etmopteridae into two

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

s, one consisting of ''

Etmopterus ''Etmopterus'' is a genus of lantern sharks in the squaliform family Etmopteridae. They are found in deep sea ecosystems of the Atlantic, Indian and Pacific Oceans. Ecology A number of species in this genus function as host to the specialized ...

'' and '' Miroscyllium'' and the other consisting of '' Centroscyllium'' and '' Aculeola''.

Phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

analyses have variously placed ''Trigonognathus'' as closer to one clade or the other or as basal to both, depending on which morphological characters,

nuclear DNA Nuclear DNA (nDNA), or nuclear deoxyribonucleic acid, is the DNA contained within each cell nucleus of a eukaryotic organism. It encodes for the majority of the genome in eukaryotes, with mitochondrial DNA and plastid DNA coding for the rest. It ...

markers, and/or

mitochondrial DNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...

markers were used. Based on

molecular clock The molecular clock is a figurative term for a technique that uses the mutation rate of biomolecules to deduce the time in prehistory when two or more life forms diverged. The biomolecular data used for such calculations are usually nucleoti ...

estimation, ''Trigonognathus'' is thought to have originated around 41 million years ago during the

Middle Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', "dawn ...

, as part of a larger

evolutionary radiation An evolutionary radiation is an increase in taxonomic diversity that is caused by elevated rates of speciation, that may or may not be associated with an increase in morphological disparity. Radiations may affect one clade or many, and be rapid ...

of etmopterid genera. The genus is represented in this time period by the

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

species '' T. virginiae'', whose

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

ized teeth have been recovered from

Lutetian The Lutetian is, in the geologic timescale, a stage or age in the Eocene. It spans the time between . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it is sometimes referred to as the Midd ...

age (47.8–41.3 Mya)

strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...

Landes ''Landes'', or ''Lanas'' in Gascon, means moorland or heath. ''Landes'' and ''Lanas'' come from the Latin ''plānus'' meaning “‘flat, even, level, plain’”. They are therefore cognate with the English plain (and plane), the Spanish word '' ...

, southwestern France. Fossil teeth virtually identical to those of the modern viper dogfish are known from the Cubagua Formation in northeastern Venezuela, which dates to the

Late Miocene The Late Miocene (also known as Upper Miocene) is a sub-epoch of the Miocene epoch (geology), Epoch made up of two faunal stage, stages. The Tortonian and Messinian stages comprise the Late Miocene sub-epoch, which lasted from 11.63 Ma (million ye ...

and

Early Pliocene Early may refer to: History * The beginning or oldest part of a defined historical period, as opposed to middle or late periods, e.g.: ** Early Christianity ** Early modern Europe Places in the United States * Early, Iowa * Early, Texas * Early ...

(11.6–3.6 Mya).

Description

The viper dogfish has a slender, cylindrical body and a moderately flattened head with a very short and blunt snout. Behind the large oval eyes are narrow, elliptical

spiracle Spiracle or spiraculum may refer to: * Spiracle (arthropods), opening in the exoskeletons of some arthropods * Spiracle (vertebrates), openings on the surface of some vertebrates * Spiraculum, a genus of land snails in family Cyclophoridae Cycl ...

s. The nostrils are nearly vertical slits. The jaws are long and narrowly triangular, and can be protruded from the head. The teeth are distinctively fang-like and widely spaced; the most anterior teeth are grooved lengthwise. Six to 10 upper and seven to 10 lower

tooth row Sharks continually shed their teeth; some Carcharhiniformes shed approximately 35,000 teeth in a lifetime, replacing those that fall out. There are four basic types of shark teeth: dense flattened, needle-like, pointed lower with triangular up ...

s occur on each side, along with a single tooth row at the upper and lower symphyses (jaw midpoints). The teeth are largest at the symphysis and decline in size towards the corners of the mouth. When the mouth is closed, the upper symphysial tooth overlaps the lower, while the lateral teeth interlock. Five

gill slit Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of cartilaginous fish such as sharks and rays, as well as deep-branching vertebrates such as lampreys. In con ...

s are seen, with the fifth pair longer than the others. The fins are small and very thin. The

pectoral fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as ...

s are rounded and lobe-like. The two

s are positioned about between the pectoral and

pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral surface of fish. The paired pelvic fins are homologous to the hindlimbs of tetrapods. Structure and function Structure In actinopterygians, the pelvic fin consists of two en ...

s. Each dorsal fin bears a slightly grooved spine in front; the second dorsal spine is longer than the first. The

anal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

is absent, and the

caudal peduncle Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

lacks keels or notches. The upper lobe of the

caudal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

is larger than the lower and has a notch in the trailing margin. The skin, excluding on the fins, is densely covered with irregularly arranged, nonoverlapping

s. Each denticle has a swollen rhombic shape with 10–40 facets on the crown. The viper dogfish is black with distinct darker markings on the underside. These markings contain large numbers of tiny light-producing

s; more photophores are found sparsely scattered over the rest of the body, as well as in a translucent patch on the upper eyelid. The fins are translucent, and the tip of the caudal fin upper lobe is blackish. The largest known male is long and weighs , and the largest female is long and weighs .

Distribution and habitat

Most specimens of the viper dogfish have been collected from a relatively small area of the northwestern Pacific Ocean off the

Kii Peninsula The is the largest peninsula on the island of Honshū in Japan. It is named after the ancient Kii Province. Overview The area south of the “ Central Tectonic Line” is called , and is home to reef-like coral communities which are amongst ...

in Japan. A number of specimens were also recovered from the stomachs of predatory fishes caught in the

. One specimen was caught from the Hancock Seamount, located some northwest of

Kure Atoll Kure Atoll (; haw, Hōlanikū, translation=bringing forth heaven; haw, Mokupāpapa, translation=flat island, label=none) or Ocean Island is an atoll in the Pacific Ocean west-northwest of Midway Atoll in the Northwestern Hawaiian Islands a ...

in the

northwestern Hawaiian Islands The Northwestern Hawaiian Islands or Leeward Hawaiian Islands are a series of islands and atolls in the Hawaiian island chain located northwest (in some cases, far to the northwest) of the islands of Kauai and Niihau. Politically, they are all p ...

. During the day, this species has been caught close to the bottom on the upper reaches of

s and

s, at depths of . At night, it has been caught between the surface and a depth of in water over deep. This pattern suggests the viper dogfish performs a

diel vertical migration Diel vertical migration (DVM), also known as diurnal vertical migration, is a pattern of movement used by some organisms, such as copepods, living in the ocean and in lakes. The word ''diel'' comes from the Latin ''dies'' day, and means a 24-h ...

, spending the day in deeper water and rising towards the surface at night; such daily movement may relate to feeding.

Biology and ecology

The viper dogfish feeds primarily on

es, notably

lanternfish Lanternfishes (or myctophids, from the Greek μυκτήρ ''myktḗr'', "nose" and ''ophis'', "serpent") are small mesopelagic fish of the large family Myctophidae. One of two families in the order Myctophiformes, the Myctophidae are represente ...

es in the genera ''

Benthosema ''Benthosema'' is a genus of lanternfishes. Species The currently recognized species in this genus are: * ''Benthosema fibulatum'' (Charles Henry Gilbert, C. H. Gilbert & Frank Cramer, Cramer, 1897) (spinycheek lanternfish) * ''Benthosema glacia ...

'' and ''

Diaphus ''Diaphus'' is a genus of lanternfish Lanternfishes (or myctophids, from the Greek μυκτήρ ''myktḗr'', "nose" and ''ophis'', "serpent") are small mesopelagic fish of the large family Myctophidae. One of two families in the order Myct ...

'', and also takes

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean group ...

s. Its long jaws and slender teeth are

adapted In biology, adaptation has three related meanings. Firstly, it is the dynamic evolutionary process of natural selection that fits organisms to their environment, enhancing their evolutionary fitness. Secondly, it is a state reached by the po ...

for grasping rather than cutting, in contrast to the short jaws and saw-like lower teeth of other dogfish sharks that are suited for excising chunks of meat. Prey is seized by a rapid extension of the jaws and swallowed whole; the shark can consume fish close to 40% as long as itself. The viper dogfish is the only dogfish species that lacks a suborbital muscle, which is normally responsible for pulling the jaws forward when biting. Jaw protrusion is instead effected by the

hyomandibula The hyomandibula, commonly referred to as hyomandibular one( la, os hyomandibulare, from el, hyoeides, "upsilon-shaped" (υ), and Latin: mandibula, "jawbone") is a set of bones that is found in the hyoid region in most fishes. It usually plays ...

r bone, which is articulated to the

skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, the ...

in a manner that allows it to swing down and forward. This unique arrangement serves to increase the distance the shark can protrude its jaws, as well as the size of its gape both vertically and horizontally. Known

predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...

s of the viper dogfish include the

bigeye tuna The bigeye tuna (''Thunnus obesus'') is a species of true tuna of the genus ''Thunnus'', belonging to the wider mackerel family Scombridae. In Hawaiian, it is one of two species known as ahi, the other being the yellowfin tuna. Bigeye tuna are f ...

(''Thunnus obesus'') and the sickle pomfret (''Taractichthys steindachneri''). Like other members of its family, this species is

viviparous Among animals, viviparity is development of the embryo inside the body of the parent. This is opposed to oviparity which is a reproductive mode in which females lay developing eggs that complete their development and hatch externally from the m ...

, giving birth to live offspring, with the developing

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

s sustained to term by

. Adult females have two functional

ovaries The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the body. T ...

and two functional

uteri The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The uteru ...

. Two of the recorded female specimens contained 25 and 26 mature

ova , abbreviated as OVA and sometimes as OAV (original animation video), are Japanese animated films and series made specially for release in home video formats without prior showings on television or in theaters, though the first part of an OVA s ...

; in the related

black dogfish The black dogfish (''Centroscyllium fabricii'') is a species of dogfish shark in the family Etmopteridae. It is common over the outer continental shelf and continental slope at depths of . Females generally inhabit deeper water than males, and ...

(''Centroscyllium fabricii''), the number of mature ova in a female is slightly greater than the number of resulting embryos, which suggests a litter size under 26 in the viper dogfish. Males and females mature sexually at roughly long, respectively.

Human interactions

The viper dogfish has no economic value. It is very infrequently caught in

commercial Commercial may refer to: * a dose of advertising conveyed through media (such as - for example - radio or television) ** Radio advertisement ** Television advertisement * (adjective for:) commerce, a system of voluntary exchange of products and s ...

s and bottom trawls targeting other species, though what effect, if any, fishing has on its population is unknown. The IUCN has listed it as Least Concern.

References

External links

"''Trigonognathus kabeyai'', Viper dogfish" at FishBase

"Species description of ''Trigonognathus kabeyai''" at Shark-References.com
{{Taxonbar, from=Q1424187 Etmopteridae Fish of the Pacific Ocean Taxa named by Kenji Mochizuki Taxa named by Fumio Ohe Fish described in 1990