Hexanchus

Hexanchus Temporal range: 196–0 Ma PreꞒ Ꞓ O S D C P T J K Pg N Sinemurian to present[1]
Bluntnose sixgill shark (Hexanchus griseus)
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
Subdivision:	Selachimorpha
Order:	Hexanchiformes
Family:	Hexanchidae
Genus:	Hexanchus Rafinesque, 1810
Type species
Hexanchus griseus[2]
Species
See text

The sixgill sharks are a genus, Hexanchus, of deepwater sharks in the family Hexanchidae. These sharks are characterized by a broad, pointed head, six pairs of gill 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).^[3] They are continental shelf-dwelling and abyssal plain scavengers with a keen sense of smell and are among the first to arrive at carrion, together with hagfish and rattails. They show a characteristic rolling motion of the head when feeding.

They have been found at depths of up to 2,500 m (8,200 ft).^{[citation needed]} 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.^[4][5]

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 moved smoothly without a defined pattern.^[6]

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.^{[clarification needed][7]}

Extant species

• Hexanchus griseus {Bonnaterre, 1788) (bluntnose sixgill shark)
• Hexanchus nakamurai Teng, 1962 (bigeyed sixgill shark)
• Hexanchus vitulus Springer & Waller, 1969 (Atlantic sixgill shark)^[4][5]

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, 1843
• Hexanchus tusbairicus Kozlov in Zhelezko & Kozlov, 1999

See also

• Shark teeth
• List of prehistoric cartilaginous fish genera

References

External links

• "Hexanchus". Integrated Taxonomic Information System. Retrieved 6 June 2006.
• Ebert, David A. (10 February 1986). "Biological Aspects of the Sixgill Shark, Hexanchus griseus". Copeia. 1986 (1): 131–135. doi:10.2307/1444898. JSTOR 1444898.
• Ebert, D.A. (June 1994). "Diet of the sixgill shark Hexanchus griseus off southern Africa". South African Journal of Marine Science. 14 (1): 213–218. doi:10.2989/025776194784287030.
• Andrews, Kelly S.; Williams, Greg D.; Farrer, Debbie; Tolimieri, Nick; Harvey, Chris J.; Bargmann, Greg; Levin, Phillip S. (August 2009). "Diel activity patterns of sixgill sharks, Hexanchus griseus: the ups and downs of an apex predator". Animal Behaviour. 78 (2): 525–536. doi:10.1016/j.anbehav.2009.05.027. S2CID 53161681.
• Cione, Alberto L.; Reguero, Marcelo (January 1994). "New records of the sharks Isurus and Hexanchus from the Eocene of Seymour Island, Antarctica". Proceedings of the Geologists' Association. 105 (1): 1–14. doi:10.1016/S0016-7878(08)80134-4.
• Large specimen filmed at 1,000 m depth (video). Archived from the original on 2021-12-21 – via YouTube.