The sixgill sawshark, ''Pliotrema warreni'' is a

sawshark A sawshark or saw shark is a member of a shark order (Pristiophoriformes ) bearing a unique long, saw-like rostrum (snout or bill) edged with sharp teeth, which they use to slash and disable their prey. There are eight species within the Pristi ...

of the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Pristiophoridae. Presence of 6 pairs of gill slits highlights this genus among sharks; outside

Hexanchiformes The Hexanchiformes are the order consisting of the most primitive types of sharks, and numbering just seven extant species. Fossil sharks that were apparently very similar to modern sevengill species are known from Jurassic specimens. Hexanchif ...

order, ''Pliotrema'' is the only shark with more than 5 gill slits. Unlike other sawsharks, the barbs on this shark's

rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ships * Ros ...

continue onto the sides of the head. Its barbels are also closer to its mouth than in other species. At maximum, females can reach over 136 cm long, and males can reach over 112 cm long.

Range and habitat

The sixgill sawshark is found in the

temperate In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout ...

and subtropical waters of the western

Indian Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by t ...

between latitudes 23° S and 37° S, at depths of between 37 and 500 m. This shark lives in the benthic and

benthopelagic The demersal zone is the part of the sea or ocean (or deep lake) consisting of the part of the water column near to (and significantly affected by) the seabed and the benthos. The demersal zone is just above the benthic zone and forms a layer of ...

zones of the continental shelf. Adults are partially segregated from juveniles, as they naturally tend to aggregate at lower depths.

Behavior

Using their sensitive barbels and electric sense, sixgill sawsharks are able to find their prey and then incapacitate them with their rostrum. Their known diet includes small fish, crustaceans, and squids. The only observed predator of the sixgill sawshark is the

tiger shark The tiger shark (''Galeocerdo cuvier'') is a species of requiem shark and the last extant member of the family Galeocerdonidae. It is a large macropredator, capable of attaining a length over . Populations are found in many tropical and tempera ...

, though it is likely other large sharks predate this species. These sharks, like other sawsharks, are

ovoviviparous Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a term used as a "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparous reproduction. Ovoviviparous animals possess embryos that develop insi ...

. They are thought to breed annually, giving birth to around five to seven pups per litter. It is possible that they come to inshore pupping grounds to give birth. The pups are around 35 cm at birth, and they later mature at around 83 cm if they are male, and around 110 cm if they are female.Compagno, Leonardo, Dando, Marc and Fowler, Sarah. Sharks of the World. Princeton University Press. 2005. pg 131-132.

Conservation

The sixgill sawshark is listed as Least Concern by the

IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biol ...

. Though they are not sought after in any market, they are frequently caught as by-catch and disposed. Because of their deep habitat, sixgill sawsharks are not considered a threat to people.

References

* {{Taxonbar, from=Q28880 Pristiophoridae Monotypic fish genera Aquitanian genus first appearances Extant Miocene first appearances Fish described in 1906

Range and habitat

Behavior

Conservation

See also

References