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

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

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 ...

in the

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 ...

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 photophores on their bodies. The members of this family are small, under long, and are ...

, and the only extant member of its

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

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

Bonin Islands The Bonin Islands, also known as the , is a list of islands of Japan, Japanese archipelago of over 30 subtropical and Island#Tropical islands, tropical islands located around SSE of Tokyo and northwest of Guam. The group as a whole has a total ...

, Pacific Ocean off northern

Taitung County Taitung () is the third largest county in Taiwan, located primarily on the island's southeastern coast and also including Green Island, Orchid Island and Lesser Orchid Island. The seat is located in Taitung City. Name While its name means "East ...

and the

Northwestern Hawaiian Islands The Northwestern Hawaiian Islands also known as the Leeward Hawaiian Islands, are a series of islands and atolls located northwest of Kauai and Niihau, Niihau in the Hawaiian Islands, Hawaiian island chain. Politically, these islands are part of ...

. 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 margi ...

s and

seamount A seamount is a large submarine landform that rises from the ocean floor without reaching the water surface (sea level), and thus is not an island, islet, or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abruptly a ...

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 on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...

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 scale (zoology), scales, which can also provide effective Underwater camouflage, camouflage through the us ...

s with faceted crowns, and numerous light-emitting

photophore A photophore is a specialized anatomical structure found in a variety of organisms that emits light through the process of boluminescence. This light may be produced endogenously by the organism itself (symbiotic) or generated through a mut ...

s concentrated on its ventral surface. Feeding mainly on

bony fish Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...

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 most animals. There are several types of skeletons, including the exoskeleton, which is a rigid outer shell that holds up an organism's shape; the endoskeleton, a rigid internal fram ...

and

muscular MUSCULAR (DS-200B), located in the United Kingdom, is the name of a surveillance program jointly operated by Britain's Government Communications Headquarters (GCHQ) and the U.S. National Security Agency (NSA) that was revealed by documents release ...

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 pregn ...

; 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 de ...

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 zone, demersal trawling. Benthic tra ...

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 (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

, measured long and was collected off

Cape Shiono A cape is a clothing accessory or a sleeveless outer garment of any length that hangs loosely and connects either at the neck or shoulders. They usually cover the back, shoulders, and arms. They come in a variety of styles and have been used thr ...

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 of 47.27 persons per km2. The total area was 117.69 km2. On March 31, 2006, Hiwasa, along with the tow ...

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

University of Tokyo The University of Tokyo (, abbreviated as in Japanese and UTokyo in English) is a public research university in Bunkyō, Tokyo, Japan. Founded in 1877 as the nation's first modern university by the merger of several pre-westernisation era ins ...

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: 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 of all kno ...

''trigonon'' ("triangle") and ''gnathus'' ("jaw"), while the

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

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 ...

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

Squaliformes The Squaliformes are an 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 membrane, and fi ...

aside from the

bramble ''Rubus'' is a large and diverse genus of flowering plants in the rose family, Rosaceae, subfamily Rosoideae, most commonly known as brambles. Fruits of various species are known as raspberries, blackberries, dewberries, and bristleberries. I ...

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 In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

s, one consisting of ''

Etmopterus ''Etmopterus'' is a genus of Etmopteridae, lantern sharks in the Squaliformes, squaliform family (biology), family Etmopteridae. They are found in deep sea ecosystems of the Atlantic Ocean, Atlantic, Indian Ocean, Indian and Pacific Oceans. Ecol ...

'' and '' Miroscyllium'' and the other consisting of ''

Centroscyllium ''Centroscyllium'' is a genus of big-eyed, deepwater dogfishes with no anal fin, a grey or black-brown body, and dorsal spines, with the second one being much larger than the first. Seven extant species are described. Species * '' Centroscylli ...

'' and ''

Aculeola The hooktooth dogfish, ''Aculeola nigra'', is a small, little-known dogfish, the only member of the genus ''Aculeola''. The type specimen is held at the National Natural History Museum, Santiago, Chile. Description The hooktooth dogfish has a ...

''.

Phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

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. ...

markers, and/or

mitochondrial DNA Mitochondrial DNA (mtDNA and mDNA) is the DNA located in the mitochondrion, mitochondria organelles in a eukaryotic cell that converts chemical energy from food into adenosine triphosphate (ATP). Mitochondrial DNA is a small portion of the 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 nucleot ...

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

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

, 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. A significantly large and diverse radiation within ...

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

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce 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 preserve ...

ized teeth have been recovered from

Lutetian The Lutetian is, in the geologic timescale, a stage (stratigraphy), stage or age (geology), 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 ...

age (47.8–41.3 Mya)

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

in Landes, 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: Places in the United States * Early, Iowa, a city * Early, Texas, a city * Early Branch, a stream in Missouri * Early County, Georgia * Fort Early, Georgia, an early 19th century fort Music * Early B, stage name of Jamaican d ...

(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 spiracles. 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 upp ...

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 c ...

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

pectoral fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish aquatic locomotion, swim. Apart from the tail or caudal fin, fish fins have no direct connection with the vertebral column ...

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 (belly) surface of fish, and are the lower of the only two sets of paired fins (the other being the laterally positioned pectoral fins). The pelvic fins are homologous to the hi ...

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 moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported o ...

is absent, and the

caudal peduncle Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

lacks keels or notches. The upper lobe of the

caudal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

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 and is located within the Kansai region. It is named after the ancient Kii Province. The peninsula has long been a sacred place in Buddhism, Shinto, and Shugendo, and many people wou ...

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 Hancock Seamount is a seamount of the Hawaiian-Emperor seamount chain in the Pacific Ocean. It was formed in the Eocene and Oligocene epochs of the Paleogene Period. The last eruption from Hancock Seamount is unknown. To the southwest is Kure A ...

, located some northwest of

Kure Atoll Kure Atoll (; ; ) or Ocean Island is an atoll in the Pacific Ocean west-northwest of Midway Atoll in the Northwestern Hawaiian Islands at . A coral ring across encloses a lagoon several meters deep. The atoll's largest island is called ''Gree ...

in the

northwestern Hawaiian Islands The Northwestern Hawaiian Islands also known as the Leeward Hawaiian Islands, are a series of islands and atolls located northwest of Kauai and Niihau, Niihau in the Hawaiian Islands, Hawaiian island chain. Politically, these islands are part of ...

. 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 adjective "diel" ( IPA: , ) comes from , and refers to a 24-hour ...

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

es in the genera '' Benthosema'' and '' Diaphus'', and also takes

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

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 p ...

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(, from , "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 a role in suspending the jaws ...

r bone, which is articulated to the

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

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 in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...

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 (biology), family Scombridae. In Hawaiian language, Hawaiian, it is one of two species known as ahi, the other being t ...

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

viviparous In animals, viviparity is development of the embryo inside the body of the mother, with the maternal circulation providing for the metabolic needs of the embryo's development, until the mother gives birth to a fully or partially developed juve ...

, giving birth to live offspring, with the developing

embryo An embryo ( ) is the initial stage of development for 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 sp ...

s sustained to term by

. Adult females have two functional

ovaries The ovary () is a gonad in the female reproductive system that produces ova; when released, an ovum travels through the fallopian tube/oviduct into the uterus. There is an ovary on the left and the right side of the body. The ovaries are endocr ...

and two functional

uteri The uterus (from Latin ''uterus'', : uteri or uteruses) 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 fertilized eggs until bir ...

. 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 special episodes of a series made specially for release in home video formats without prior showings on television or in theaters, though the ...

; in the related

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

(''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 Sexual maturity is the capability of an organism to reproduce. In humans, it is related to both puberty and adulthood. ''Puberty'' is the biological process of sexual maturation, while ''adulthood'', the condition of being socially recognized as ...

at roughly long, respectively.

Human interactions

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

commercial Commercial may refer to: * (adjective for) commerce, a system of voluntary exchange of products and services ** (adjective for) trade, the trading of something of economic value such as goods, services, information or money * a dose of advertising ...

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