Isistius

Isistius

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Encyclopedia
Isistius is a genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of dogfish sharks
Squaliformes
Squaliformes is an order of sharks that includes about 97 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 family
Family (biology)
In 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. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Dalatiidae
Dalatiidae
Dalatiidae 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...

. They are commonly known as cookiecutter shark
Cookiecutter shark
The cookiecutter shark , also called the cigar shark, is a species of small dogfish shark in the family Dalatiidae. This shark occurs in warm, oceanic waters worldwide, particularly near islands, and has been recorded from as deep as . It migrates vertically up to every day, approaching the...

s. Members of the genus are known for their unusual behaviour and dentition.

Species

  • Isistius brasiliensis (Quoy
    Jean René Constant Quoy
    Jean René Constant Quoy was a French zoologist.Along with Joseph Paul Gaimard he served as naturalist aboard La Coquille under Louis Isidore Duperrey during its circumnavigation of the globe , and the Astrolabe under the command of Jules Dumont d'Urville...

     & Gaimard
    Joseph Paul Gaimard
    Joseph Paul Gaimard was a French naval surgeon and naturalist.Along with Jean René Constant Quoy he served as naturalist on the ships L'Uranie under Louis de Freycinet 1817-1820, and L'Astrolabe under Jules Dumont d'Urville 1826-1829...

    , 1824)
    (Cookiecutter shark)
  • Isistius labialis Q. W. Meng, Y. T. Zhu & S. Li, 1985 (South China cookiecutter shark)
  • Isistius plutodus Garrick & S. Springer
    Stewart Springer
    Stewart 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,...

    , 1964
    (Largetooth cookiecutter shark)

Habits


The cookiecutter shark
Cookiecutter shark
The cookiecutter shark , also called the cigar shark, is a species of small dogfish shark in the family Dalatiidae. This shark occurs in warm, oceanic waters worldwide, particularly near islands, and has been recorded from as deep as . It migrates vertically up to every day, approaching the...

s, or 'cigar sharks' are noted as a genus of sharks that are unusual in the manner in which they replace their teeth. Instead of replacing teeth singly as they get damaged or lost, for example in hunting, such sharks replace the whole set. They can repeat such replacement throughout their lifetime.
Cookiecutter sharks often attack large shoals of fish, but have been known to circle fishing vessels in order to get an easy meal. It is particularly notorious for biting small chunks off of a prey animal in passing. Large prey such as swordfish
Swordfish
Swordfish , also known as broadbill in some countries, are large, highly migratory, predatory fish characterized by a long, flat bill. They are a popular sport fish of the billfish category, though elusive. Swordfish are elongated, round-bodied, and lose all teeth and scales by adulthood...

 and cetaceans, may bear several healed wounds from such bites.

Weaker prey may be injured enough to be weakened until they are unable to swim properly. They then are prone to sinking, enabling the Isistius to gorge. Isistius species can eat half of their own body weight at a time and are found in oceanic waters.

In unusual circumstances, cookiecutter sharks have been known to attack humans if they find them in their hunting grounds, and there even have been reports of of their killing humans, circling them in great numbers while stripping their flesh.