The largetooth cookiecutter shark (''Isistius plutodus'') 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), ...

of squaliform shark 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 ...

Dalatiidae The Dalatiidae are the family of kitefin sharks of the order Squaliformes (the term "kitefin shark" also refers specifically to the species '' Dalatias licha''). Members of this family are small, under long, and are found worldwide. They have c ...

, reported from depths of at scattered locations in the

Atlantic The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for se ...

and

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...

s. As its

common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often con ...

suggests, it is similar in appearance to the

cookiecutter shark The cookiecutter shark (''Isistius brasiliensis''), also called the cigar shark, is a species of small squaliform shark in the family Dalatiidae. This shark lives in warm, oceanic waters worldwide, particularly near islands, and has been reco ...

(''I. brasiliensis'') but has much larger lower teeth. This species reaches a maximum known length of . The largetooth cookiecutter shark feeds by gouging out chunks of flesh from larger animals, including

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, sharks, and

marine mammal Marine mammals are mammals that rely on marine ecosystems for their existence. They include animals such as cetaceans, pinnipeds, sirenians, sea otters and polar bears. They are an informal group, unified only by their reliance on marine enviro ...

s, and is able to take larger bites than ''I. brasiliensis''. Little is known of its life history; it is thought to be a weaker swimmer than ''I. brasiliensis'', and is presumably

aplacental viviparous Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparous reproduction. Ovoviviparous animals possess embryos that develop inside eggs that rema ...

like the rest of its family. This shark is an infrequent

bycatch Bycatch (or by-catch), in the fishing industry, is a fish or other marine species that is caught unintentionally while fishing for specific species or sizes of wildlife. Bycatch is either the wrong species, the wrong sex, or is undersized or juve ...

of commercial

trawl Trawling is an industrial method of fishing that involves pulling a fishing net through the water behind one or more boats. The net used for trawling is called a trawl. This principle requires netting bags which are towed through water to catch di ...

and longline

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 ...

, but is not thought to be much threatened by these activities.

Taxonomy

The largetooth cookiecutter shark was originally described by

Jack Garrick John Andrew Frank Garrick (24 March 1928 – 30 August 2018) was a New Zealand ichthyologist. Career Garrick specialised in elasmobranchs and published many books and articles about shark and ray biology. In 1982, he published a thorough taxonom ...

and

Stewart Springer Stewart Springer (5 June 190623 August 1991) was an American ichthyologist and herpetologist. He was an expert on shark behavior, classification (taxonomy), and population distribution. More than 35 species of sharks, skates, rays, and other cr ...

, in a 1964 issue of the

scientific journal In academic publishing, a scientific journal is a periodical publication designed to further the progress of science by disseminating new research findings to the scientific community. These journals serve as a platform for researchers, schola ...

''Copeia''. Their description was based on a long adult female caught in a midwater

in the

Gulf of Mexico The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...

, some south of

Dauphin Island Dauphin Island, formerly Massacre Island (French language, French: ''Île du Massacre'') is an island town in Mobile County, Alabama, Mobile County, Alabama, United States, on a barrier island of the same name, in the Gulf of Mexico. It incorpora ...

Alabama Alabama ( ) is a U.S. state, state in the Southeastern United States, Southeastern and Deep South, Deep Southern regions of the United States. It borders Tennessee to the north, Georgia (U.S. state), Georgia to the east, Florida and the Gu ...

. The

specific epithet In Taxonomy (biology), taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin gramm ...

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 ...

("wealth" or "abundance") and ("tooth"). This species may also be referred to as the bigtooth or longtooth cookiecutter shark, or the Gulf dogfish.

Distribution and habitat

Much rarer than ''I. brasiliensis'', only ten specimens of largetooth cookiecutter shark are known, caught from a handful of widely scattered localities: off Alabama in the United States,

Bahia Bahia () is one of the 26 Federative units of Brazil, states of Brazil, located in the Northeast Region, Brazil, Northeast Region of the country. It is the fourth-largest Brazilian state by population (after São Paulo (state), São Paulo, Mina ...

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

, the

Azores The Azores ( , , ; , ), officially the Autonomous Region of the Azores (), is one of the two autonomous regions of Portugal (along with Madeira). It is an archipelago composed of nine volcanic islands in the Macaronesia region of the North Atl ...

, and

Western Sahara Western Sahara is a territorial dispute, disputed territory in Maghreb, North-western Africa. It has a surface area of . Approximately 30% of the territory () is controlled by the Sahrawi Arab Democratic Republic (SADR); the remaining 70% is ...

in the

Atlantic Ocean The Atlantic Ocean is the second largest of the world's five borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...

, and off

Okinawa most commonly refers to: * Okinawa Prefecture, Japan's southernmost prefecture * Okinawa Island, the largest island of Okinawa Prefecture * Okinawa Islands, an island group including Okinawa itself * Okinawa (city), the second largest city in th ...

and

New South Wales New South Wales (commonly abbreviated as NSW) is a States and territories of Australia, state on the Eastern states of Australia, east coast of :Australia. It borders Queensland to the north, Victoria (state), Victoria to the south, and South ...

in the

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...

. Those captures were made in the

epipelagic zone The photic zone (or euphotic zone, epipelagic zone, or sunlight zone) is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological ...

down, close to land over

continental shelves A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...

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, or

oceanic trench Oceanic trenches are prominent, long, narrow topography, topographic depression (geology), depressions of the seabed, ocean floor. They are typically wide and below the level of the surrounding oceanic floor, but can be thousands of kilometers ...

es that may descend as far as . The shark's rarity may be due to a restricted distribution or, more likely, it normally preferring deeper waters.

Description

The largetooth cookiecutter shark has a long, cigar-shaped body with an extremely short, blunt head and snout. The large, oval eyes are positioned to allow

binocular vision Binocular vision is seeing with two eyes. The Field_of_view, field of view that can be surveyed with two eyes is greater than with one eye. To the extent that the visual fields of the two eyes overlap, #Depth, binocular depth can be perceived. Th ...

, and are followed by wide, angled spiracles. The

nostril A nostril (or naris , : nares ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbinates ...

s are small, each with a low, pointed skin lobe in front. The mouth is transverse, with a deep fold enclosing its corners and fleshy suctorial lips. The jaws are larger and more powerful than those of ''I. brasiliensis'', and contain fewer tooth rows, numbering around 29 in the upper jaw and 19 in the lower jaw. The upper teeth are small, narrow, and smooth-edged, upright at the center of the jaw and becoming more angled towards the corners. The lower teeth are massive, the largest teeth relative to body size of any living shark. They are triangular in shape, with minutely serrated edges and interlocking rectangular bases. The five pairs of

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 minute. The small

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 ...

s have rounded apices and are placed far back, on the last third of the body. The first dorsal fin originates slightly ahead of the

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, while the second dorsal originates closely behind and measures almost a third again the height of the first. 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 small and rounded, and positioned relatively high on the body behind the fifth gill slit. The pelvic fins are tiny, and there is no

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 ...

. The caudal fin is very short, with the upper lobe twice as long as the lower and bearing a prominent ventral notch near the tip. The coloration is a plain dark brown, with translucent margins on the fins and sparsely scattered 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 on the belly. Some specimens have lacked the dark "collar" found on the throat of ''I. brasiliensis''. However, a specimen caught in 2004 off the Azores did possess the collar, and other freshly caught specimens also possess this trait, suggesting that the lack of a collar is an artifact of preservation. The maximum recorded length is .

Biology and ecology

Based on its smaller dorsal and caudal fins, the largetooth cookiecutter shark is believed to be less active than ''I. brasiliensis'' and an overall weak swimmer. Much of its body cavity is occupied by an enormous

oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) and lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturate ...

-filled

liver The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...

, which allows it to maintain

neutral buoyancy Neutral buoyancy occurs when an object's average density is equal to the density of the fluid in which it is immersed, resulting in the buoyant force balancing the force of gravity that would otherwise cause the object to sink (if the body's de ...

in the water column with little effort. Unlike ''I. brasiliensis'', this shark possesses binocular vision, which may allow it to target its prey with greater precision. Virtually nothing is known of its biology; it is presumed to be

. Like ''I. brasiliensis'', the largetooth cookiecutter shark is an

ectoparasite Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted str ...

that feeds by excising plugs of flesh from larger animals. While ''I. brasiliensis'' is theorized to latch onto the surface of its prey and bite with a twisting motion, producing a circular wound containing spiral grooves inside from its lower teeth, the largetooth cookiecutter shark seems to employ a "sweeping" bite that produces a larger, more elongate (twice as long as the width of the mouth), oval wound containing parallel tooth grooves. This shark has been known to bite bony fishes, sharks, and marine mammals. One study has found that the largetooth cookiecutter shark is responsible for 80% of the cookiecutter wounds found on

cetacean Cetacea (; , ) is an infraorder of aquatic mammals belonging to the order Artiodactyla that includes whales, dolphins and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively c ...

s off Bahia, Brazil. The flank was the most often-attacked area, followed by the head and abdomen. In at least three cases, bites to

dolphin A dolphin is an aquatic mammal in the cetacean clade Odontoceti (toothed whale). Dolphins belong to the families Delphinidae (the oceanic dolphins), Platanistidae (the Indian river dolphins), Iniidae (the New World river dolphins), Pontopori ...

s appeared to have resulted in their subsequent deaths by stranding. Another prey species in the area is the

subantarctic fur seal The subantarctic fur seal (''Arctocephalus tropicalis'') is a species of arctocephaline found in the southern parts of the Indian, Pacific, and Atlantic Oceans. It was first described by Gray in 1872 from a specimen recovered in northern Austra ...

(''Arctocephalus tropicalis''); at least two cases of juveniles fatally stranding after being bitten have also been recorded.

Human interactions

Other than possibly damaging

billfish The billfish are a group (Xiphioidea) of saltwater fish, saltwater predatory fish characterised by prominent pointed beak, bills (rostrum (anatomy), rostra), and by their large size; some are longer than . Extant billfish include sailfish and m ...

es or other valued species, the largetooth cookiecutter shark is of no import to

commercial fisheries Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often p ...

. All but one of the known specimens have been caught as

in commercial trawls or longlines. However, given the infrequency of these catches and this species' probable wide distribution, the

International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the stat ...

(IUCN) has assessed it as of

Least Concern A least-concern species is a species that has been evaluated and categorized by the International Union for Conservation of Nature (IUCN) as not being a focus of wildlife conservation because the specific species is still plentiful in the wil ...

References

{{Taxonbar, from=Q1420774 Isistius Bioluminescent sharks Deep sea fish Fish described in 1964