Hexanchus vitulus

Hexanchus vitulus
Hexanchus vitulus , image from the Gulf of Mexico
Systematics
without rank: Sharks (selachii) Superordinate : Squalomorphii Order : Hexanchiformes Family : Comb tooth sharks (Hexanchidae) Genre : Six-gill sharks ( Hexanchus ) Type : Hexanchus vitulus
Scientific name
Hexanchus vitulus
Springer & Waller , 1969

Hexanchus vitulus ( English atlantic sixgill shark ) is a so far little researched shark species from the order of the Hexanchiformes . It occurs in the tropical western Atlantic ( Caribbean , Gulf of Mexico ) at depths of 90 to 350 meters.

features

Compared to the snub -nosed six- gill shark ( Hexanchus griseus ), which grows to more than 5 meters , Hexanchus vitulus is a small species of shark. It becomes sexually mature with a length of 1.4 to 1.75 m and possibly no longer than 1.8 m. The fish are colored solid gray, without any drawings or patterns. Only the belly is a little lighter. They have proportionally larger eyes and a longer snout (in fish the distance from the front edge of the eye to the tip of the head) than Hexanchus griseus . The distance between the base of the dorsal and anal fin and the base of the caudal fin is also proportionally larger. The distal edge of the pectoral fins is concave in Hexanchus vitulus . The lower caudal fin lobe is more developed in young Hexanchus vitulus than in young snub -nosed six- gill sharks. In the lower jaw, Hexanchus vitulus has five rows of large trapezoidal teeth (six in Hexanchus griseus ).

Systematics

With these characteristics, Hexanchus vitulus can hardly be distinguished from the big-eyed six- gill shark ( Hexanchus nakamurai ) with which the species was synonymous in the past . However, a comparison of 1310 base pairs from the mitochondrial DNA of six gill sharks from the tropical western Atlantic and that of bigeye six gill sharks from the Pacific (Japan) and the Indian Ocean (Reunion and Madagascar) showed a genetic distance of 7.037%. Since this is roughly the same as the genetic distance between the snub-nosed six-gill shark and the bigeye six-gill shark (8.2%), as well as between the genus Hexanchus and its sister genus Heptranchias (8.308%), Hexanchus vitulus was chosen in February 2018 for the small six-gill sharks revalidated from the tropical western Atlantic.

Individual evidence

1. ^ Stewart Springer, Richard A. Waller: Hexanchus vitulus, a New Sixgill Shark from the Bahamas . Bulletin of Marine Science, Volume 19, Number 1, March 1969, pp. 159-174 (16)
2. ↑ Daly-Engel, TS, Baremore, IE, Grubbs, RD, Gulak, SJB, Graham, RT & Enzenauer, MP (2018): Resurrection of the sixgill shark Hexanchus vitulus Springer & Waller, 1969 (Hexanchiformes, Hexanchidae), with comments on its distribution in the northwest Atlantic Ocean. Marine Biodiversity, February 2018. doi: 10.1007 / s12526-018-0849-x