Big tooth cigar shark

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Big tooth cigar shark
Systematics
without rank: Sharks (selachii)
Superordinate : Squalomorphii
Order : Spiny dogfish (Squaliformes)
Family : Dalatiidae
Genre : Cigar sharks ( Isistius )
Type : Big tooth cigar shark
Scientific name
Isistius Plutodus
Garrick & Springer , 1964

The big-tooth cigar shark ( Isistius plutodus ) is - next to the cigar shark ( Isistius brasiliensis ) - the second of the three species in the genus of cigar sharks . Of all living sharks , big-tooth cigar sharks have the largest teeth in proportion to their body. They live as short-term ectoparasites on larger fish and marine mammals . Almost nothing is known about their distribution and lifestyle.

anatomy

Big-tooth cigar sharks are one of the smallest shark species with an estimated maximum length of 50 cm. The longest specimen so far was a not yet sexually mature male with a length of 42 cm. The species owes its name on the one hand to the spindle-shaped body and on the other hand to the large, triangular teeth in the lower jaw.

The animals are brown in color with a dark spot on the ventral side below the gills. They each have a pair of pectoral and pelvic fins, two dorsal fins of approximately the same size, which lie far at the end of the back, and an "asymmetrical" caudal fin: with a significantly larger upper lobe, which - like all other fins - is not contrasted in color from the body .

The snout of the big-tooth cigar shark is very short, the eyes look forward and thus presumably enable the animal to see three-dimensionally. They usually have 38 to 48 teeth, 21 to 29 of which are in the upper jaw and the remaining 17 to 19 teeth are in the lower jaw. The maxillary teeth are thorn-like, the mandibular teeth wide and triangularly pointed towards the top.

Like the cigar shark, Isistius plutodus is bioluminescent , which means that it has the ability to glow. The scientific generic name Isistius , which is derived from Isis , the Egyptian goddess of light, takes this fact into account . The underside of the body is covered with thousands of very small luminous organs , so-called photophores , which have a diameter between 0.03 and 0.05 mm. Presumably this ability plays a crucial role in food production.

behavior

The two types of cigar sharks are probably not good swimmers due to their physical nature. Like all sharks, they do not have a swim bladder . Another specialty is the partial calcification of the cranial cartilage and the jaw apparatus. This additional weight, which actually makes it difficult to keep yourself in suspension, is compensated for by the extraordinarily large and oil-containing liver, which fills almost the entire abdominal cavity.

distribution

Distribution areas of the big-tooth cigar shark

The so far only isolated finds of big-tooth cigar sharks in the Gulf of Mexico , off Okinawa or Australia do not allow any reliable conclusions to be drawn about the geographical distribution of the species. Presumably it is an open ocean fish.

"The few specimens are widely scattered, and it is assumed that they tend to live at greater depths or that only a small number of animals exist." (Compagno (1984), loc. Cit: Zidowitz (2003))

It is believed that the animals cover a daily migration cycle in the water column, which extends from a depth of 3,500 m to the surface.

Reproduction

Whether big-tooth cigar sharks are viviparous is as little known as their reproduction habits or their breeding areas.

Diet

Bioluminescence in particular enables the animals to live their special parasitic way of life, but does not - unlike other fish in the deep sea, such as deep-sea frogfish - serve to attract the prey directly, but actually as camouflage: the glow on the belly lets it The shark's silhouette becomes invisible against the surface of the water, which is the brightest light source in its habitat. Only the dark spot of the gill region remains visible against the surface and thus simulates a smaller fish to a larger predator. The predator attracted in this way now becomes a victim of the large-tooth cigar shark, which bites its skin with its needle-pointed, inwardly curved upper jaw teeth and uses the lower jaw teeth, which are used like a punch ring, to cut a conical piece of meat from its prey. The English name for Largetooth cookiecutter shark (German: large tooth cookie cutter shark ) takes this way of life into account. No specimen of the cigar shark has been observed alive so far, so that the description of their feeding behavior can be presented conclusively, but has not been empirically proven.

literature

  • Compagno, LJV (1984): FAO species catalog. Vol 4, Sharks of the world. An annotated and illustrated catalog of shark species known to date. Part I - Hexanchiformes to Lamniformes: viii, 1-250. FAO Fisheries Synopsis 125: 1-249.
  • JAF Garrick, Stewart Springer: Isistius plutodus, a New Squaloid Shark from the Gulf of Mexico . In: Copeia . tape 1964 , no. 4 , December 1964, p. 678-682 , doi : 10.2307 / 1441443 .
  • McGrouther, MA (2001): First record of the Large-tooth Cookie-Cutter Shark, Isistius plutodus from Australian waters. In: Memoirs of the Queensland Museum 46 (2): p. 442 ( online ).
  • H. Zidowitz, HO Fock, C. Pusch, H. von Westernhagen: A first record of Isistius plutodus in the north-eastern Atlantic . In: Journal of Fish Biology . tape 64 , no. 5 , May 2004, pp. 1430-1434 , doi : 10.1111 / j.0022-1112.2004.00382.x .

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