The
largetooth cookiecutter shark,
Isistius plutodus, is a rare
speciesIn biology, a species is:* a taxonomic rank or* a unit at that rank ....
of
dogfish sharkSqualiformes is an order of sharks that includes about 80 species in seven families.Members of the order have two dorsal fins, which usually possess spines, no anal fin or nictitating membrane, and five gill slits. In most other respects, however, they are quite variable in form and size...
in the
familyIn biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus...
DalatiidaeDalatiidae is a family of sharks in the order Squaliformes, commonly known as kitefin sharks . Members of this family are small, under long, and are found worldwide. They have cigar-shaped bodies with narrow heads and rounded snouts...
, reported from depths of at scattered locations in the Atlantic and
Pacific OceanThe Pacific Ocean is the largest of the Earth's oceanic divisions. Its name is derived from the Latin name Tepre Pacificum, "peaceful sea", bestowed upon it by the Portuguese explorer Ferdinand Magellan. It extends from the Arctic in the north to Antarctica in the south, bounded by Asia and...
s. As its
common nameA common name is a name in general use within a community; it is often contrasted with a scientific name...
suggests, it is similar in appearance to the
cookiecutter sharkThe cookiecutter shark, Isistius brasiliensis, also known as the cigar shark or luminous shark, is a small, rarely-seen dogfish shark.-Anatomy and morphology:...
(
I. brasiliensis) but has much larger lower teeth. Most individuals also lack the dark "collar" of
I. brasiliensis. This species reaches a maximum known length of . The largetooth cookiecutter shark feeds by gouging out chunks of flesh from larger animals, including bony fishes, sharks, and
marine mammalMarine mammals are a diverse group of roughly 120 species of mammal that are primarily ocean-dwelling or depend on the ocean for food. They include the cetaceans , the sirenians , the pinnipeds , and several otters...
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 ovoviviparous like the rest of its family. This shark is an infrequent bycatch of commercial trawl and longline fisheries, but is not thought to be much threatened by these activities.
Taxonomy
The largetooth cookiecutter shark was originally described by
New ZealandNew Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses , and numerous smaller islands, most notably Stewart Island/Rakiura and the Chatham Islands. The indigenous Māori named New Zealand Aotearoa, commonly translated as The Land of the Long White Cloud...
ichthyologist Jack Garrick and
AmericanThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
sharkSharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago, before the time of the dinosaurs....
expert
Stewart SpringerStewart Springer, was a world renowned expert on shark behavior, classification , and distribution of shark populations. There are more than 35 species of sharks, skates, rays, and other animals either classified originally by him or named after him.-Education:Springer was a field naturalist,...
, in a 1964 issue of the
scientific journalIn academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research. There are thousands of scientific journals in publication, and many more have been published at various points in the past...
Copeia. Their description was based on a long adult female caught in a midwater trawl in the
Gulf of MexicoThe Gulf of Mexico is the ninth largest body of water in the world. Considered a smaller part of the Atlantic Ocean, it is an ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United...
some south of Dauphin Island,
AlabamaAlabama is a state located in the southeastern region of the United States of America. It is bordered by Tennessee to the north, Georgia to the east, Florida and the Gulf of Mexico to the south, and Mississippi to the west. Alabama ranks 30th in total land area and ranks second in the size of its...
. The specific epithet
plutodus is derived from the Greek
ploutos meaning "wealth" or "abundance", and
odous meaning "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 the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
(Alabama),
BrazilBrazil , officially the Federative Republic of Brazil , is a country in South America. It is the fifth largest country by geographical area, occupying nearly half of South America, the fifth most populous country, and the fourth most populous democracy in the world. Bounded by the Atlantic Ocean...
(
BahiaBahia is one of the 26 states of Brazil, and is located in the northeastern part of the country on the Atlantic coast.It is the fourth most populous Brazilian state after São Paulo, Minas Gerais and Rio de Janeiro, and the fifth-largest in size...
),
PortugalPortugal , officially the Portuguese Republic , is a country located in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of mainland Europe and is bordered by the Atlantic Ocean to the west and south and by Spain to the north and east...
(the
AzoresThe Azores is a Portuguese archipelago in the Atlantic Ocean, about from Lisbon and about from the east coast of North America. The two westernmost Azorean islands actually lie on the North American plate...
), and
Western SaharaWestern Sahara is a territory of North Africa, bordered by Morocco to the north, Algeria to the northeast, Mauritania to the east and south, and the Atlantic Ocean to the west. Its surface area amounts to . It is one of the most sparsely populated territories in the world, mainly consisting of...
in the Atlantic, and off
Japanis an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, People's Republic of China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
(Okinawa) and
AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the continental mainland , the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans...
(
New South WalesNew South Wales is Australia's most populous state, located in the south-east of the country, north of Victoria, south of Queensland and east of South Australia...
) in the Pacific. These captures have been made in the epipelagic zone down, close to land from over continental shelves to over continental slopes or
oceanic trenchThe oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor. They are also the deepest parts of the ocean floor....
es that may descend as far as . This 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 visionBinocular vision is vision in which both eyes are used together. The word binocular comes from two Latin roots, bini for double, and oculus for eye. Having two eyes confers at least four advantages over having one. First, it gives a creature a spare eye in case one is damaged. Second, it gives a...
, and are followed by wide, angled
spiracleSpiracles are small openings on the surface of some animals that usually lead to respiratory systems.In elasmobranchs , a spiracle is found behind each eye, and is often used to pump water through the gills while the animal is at rest .-Spiracles in insects:Insects and some more advanced spiders...
s. The
nostrilA nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
s are small, each with a low, pointed skin lobe in front. The mouth is transverse, with a deep fold enclosing its corners and fleshy
suctorialSuctorial pertains to the adaptation for sucking or suction, as possessed by marine parasites such as the Cookiecutter shark, specifically in a specialised lip organ enabling attachment to the host....
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 slitGill 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, rays, sawfish, and guitarfish. Most of these have five pairs, but a few species have 6 or 7 pairs...
s are minute.
The small
dorsal finA dorsal fin is a fin located on the backs of some fish, whales, dolphins, and porpoises, as well as the ichthyosaurs. Depending on the species, an animal can have up to three of them. Its main purpose is to stabilize the animal against rolling and assist in sudden turns...
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 fins, while the second dorsal originates closely behind and measures almost a third again the height of the first. The pectoral fins 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. 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-emittingBioluminescence is the production and emission of light by a living organism. Its name is a hybrid word, originating from the Greek bios for "living" and the Latin lumen "light". Bioluminescence is a naturally occurring form of chemiluminescence where energy is released by a chemical reaction in...
photophoreA photophore is a light-emitting organ which 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 on the belly. Most 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. 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
oilShark liver oil is obtained from sharks that are caught for food purposes and are living in cold, deep oceans. The liver oil from sharks has been used by fishermen for centuries as a folk remedy for general health. It is purportedly useful for healing wounds, sores, irritations of the respiratory...
-filled
liverThe liver is a vital organ present in vertebrates and some other animals; it has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
, which allows it to maintain
neutral buoyancyNeutral buoyancy is a condition in which a physical body's mass equals the mass it displaces in a surrounding medium. This offsets the force of gravity that would otherwise cause the object to sink...
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 ovoviviparous.
Like
I. brasiliensis, the largetooth cookiecutter shark is an ectoparasite 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 cetaceans off Bahia, Brazil. The flank was the most often-attacked area, followed by the head and abdomen. In at least three cases, bites to
dolphinDolphins are marine mammals that are closely related to whales and porpoises. There are almost forty species of dolphin in seventeen genera. They vary in size from and , up to and . They are found worldwide, mostly in the shallower seas of the continental shelves, and are carnivores, mostly...
s appeared to have resulted in their subsequent deaths by stranding. Another prey species in the area is the
subantarctic fur sealThe Subantarctic Fur Seal is a fur seal found in the southern parts of the Indian and Atlantic Oceans. It was first described by Gray in 1872 from a specimen recovered in northern Australia—hence the inappropriate tropicalis specific name.-Description:The Subantarctic Fur Seal is...
(
Arctocephalus tropicalis); at least two cases of juveniles fatally stranding after being bitten have also been recorded.
Human interactions
Other than possibly damaging
billfishThe term billfish is applied to a number of different large, predatory fish characterised by their large size and their long, sword-like bill. Billfish include the sailfish and marlin, which make up the family Istiophoridae, and the swordfish, sole member of the family Xiphiidae...
es or other valued species, the largetooth cookiecutter shark is of no import to
commercial fisheriesCommercial fishing is the activity of capturing 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 pursue fish far into the ocean under adverse...
. All but one of the known specimens have been caught as bycatch 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 (IUCN) has assessed it as of
Least ConcernLeast Concern is an IUCN category assigned to extant species or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, nor Near Threatened, nor Conservation Dependent...
.