The sixgill sharks are a genus, ''Hexanchus'', of deepwater

shark Sharks are a group of elasmobranch cartilaginous fish characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the ...

s 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 ...

Hexanchidae. These sharks are characterized by a broad, pointed head, six pairs of

gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow r ...

slits, comb-like, yellow lower teeth, and a long tail. The largest species can grow up to 8 m long and weigh over 600 kg (1320 lb). They are continental shelf-dwelling and

abyssal plain An abyssal plain is an underwater plain on the deep ocean floor, usually found at depths between . Lying generally between the foot of a continental rise and a mid-ocean ridge, abyssal plains cover more than 50% of the Earth's surface. They ...

scavengers with a keen sense of smell and are among the first to arrive at carrion, together with

hagfish Hagfish, of the Class (biology), class Myxini (also known as Hyperotreti) and Order (biology), order Myxiniformes , are eel-shaped Agnatha, jawless fish (occasionally called slime eels). Hagfish are the only known living Animal, animals that h ...

and rattails. They show a characteristic rolling motion of the head when feeding. They have been found at depths of up to . Though only two extant species (the bluntnose sixgill shark and the bigeyed sixgill shark) were originally known, a third, the Atlantic sixgill shark, was found to exist.

Swimming behavior

The bluntnose sixgill shark, ''Hexanchus griseus'', is relatively common to scientists. However, very little information exists about its distribution patterns, migrations and behavior. Data on occurrence and behavior of sixgill sharks inhabiting waters north of Spain (Galicia and Cantabrian Sea, NE Atlantic) were obtained from yearly oceanographic trawl surveys. Data obtained from one electronic pop-up tag (Mini PAT), provided information about depth and temperature preferences over 75 days. Mean depth obtained during that period was 913 m (depth range 727–1247 m), and the mean temperature was 10.3 °C, (range 8.0–10.8 °C). Movements up and down in the water column within a single day ranged from 50 to 385 m. No cyclic diel vertical migration was however observed, the shark having moved smoothly without a defined pattern. The six-gill sharks have the ability to alter their feeding behaviors due to the situation that they are in. A feeding behavior analysis displayed that the six-gill sharks are able to utilize a bite of food compared to other aquatic vertebrates.

Extant species

* '' Hexanchus griseus '' ( Bonnaterre, 1788) (bluntnose sixgill shark) * '' Hexanchus nakamurai'' Teng, 1962 (bigeyed sixgill shark) *'' Hexanchus vitulus''

Springer Springer or springers may refer to: Publishers * Springer Science+Business Media, aka Springer International Publishing, a worldwide publishing group founded in 1842 in Germany formerly known as Springer-Verlag. ** Springer Nature, a multinationa ...

& Waller, 1969 (Atlantic sixgill shark)

Extinct species

* '' Hexanchus agassizi'' Cappetta, 1976 * '' Hexanchus andersoni'' Jordan, 1907 * '' Hexanchus casieri'' Kozlov, 1999 * '' Hexanchus collinsonae'' Ward, 1979 * '' Hexanchus gracilis'' Davis, 1887 * '' Hexanchus hookeri'' Ward, 1979 * '' Hexanchus microdon''

Agassiz Jean Louis Rodolphe Agassiz ( ; ) FRS (For) FRSE (May 28, 1807 – December 14, 1873) was a Swiss-born American biologist and geologist who is recognized as a scholar of Earth's natural history. Spending his early life in Switzerland, he recei ...

, 1843 * '' Hexanchus tusbairicus'' Kozlov in Zhelezko & Kozlov, 1999 Records earlier than

Albian The Albian is both an age (geology), age of the geologic timescale and a stage (stratigraphy), stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early Cretaceous, Early/Lower Cretaceous epoch (geology), Epoch/s ...

such as

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. ...

species ''H. arzoensis'' and ''H. wiedenrothi'' are later considered as misidentification, the first moved to '' Notidanoides'' and later moved to ''

Crassodontidanus ''Crassodontidanus'' is an extinct genus of sharks and the sole member of the family Crassodontidanidae, in the order Hexanchiformes. It contains two extinct species.A new Jurassic cow shark (Chondrichthyes, Hexanchiformes) with comments on Juras ...

''.

References

External links

* * * * * * {{Authority control Albian genus first appearances Extant Early Cretaceous first appearances Shark genera Taxa named by Constantine Samuel Rafinesque

Swimming behavior

Extant species

Extinct species

See also

References

External links