The daggertooth (''Anotopterus pharao'', meaning "without fins on its back, of the Pharaoh") is a species of daggertooth. Its distribution includes the

North Atlantic Ocean The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for se ...

and west of

Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

. The record size for this species is 96 cm and was hermaphroditic. Daggertooths are occasionally found dead in bottom trawls used for firefly squid or

shrimp A shrimp (: shrimp (American English, US) or shrimps (British English, UK)) is a crustacean with an elongated body and a primarily Aquatic locomotion, swimming mode of locomotion – typically Decapods belonging to the Caridea or Dendrobranchi ...

. They are similar to

needlefish Needlefish (family Belonidae) or long toms are piscivorous fishes primarily associated with very shallow marine habitats or the surface of the open sea. Some genera include species found in marine, brackish, and freshwater environments (e.g., ...

or gars. However, they are distinct. Netted daggertooth specimens are rarely identifiable, mostly because of their soft bodies, which are easily torn or flattened. This is typical of

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...

animals of the deep ocean, like some transparent squids. In fact, the bodies are so soft, when pushed against the back of a trawl net, they often die because their organs are crushed and they rip. The habitat of the daggertooth is the open abyss, where few obstacles occur with which to come into physical contact.

Metamorphosis

The species undergoes

metamorphosis Metamorphosis is a biological process by which an animal physically develops including birth transformation or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and different ...

, whereupon they become black in colour, become toothless, stop feeding, develop very large gonads and the gastrointestinal tract atrophies. This was discovered in 1971, after German ichthyologist

Günther Maul Günther Edmund Maul (May 7, 1909 – September 28, 1997) was a German ichthyologist and taxidermist in Portugal. Maul came to Madeira in December 1930 to work as taxidermist at Museu Municipal do Funchal, which opened to the public in 1933. He w ...

caught such a specimen off

Madeira Madeira ( ; ), officially the Autonomous Region of Madeira (), is an autonomous Regions of Portugal, autonomous region of Portugal. It is an archipelago situated in the North Atlantic Ocean, in the region of Macaronesia, just under north of ...

that measured 75.9 cm. It was posited that there may be a vertical downwards migration at this final short stage of life. The reduced light at this increased depth may have selected for the black colouration. As ''Anotopterus'' quickly shed and replace their teeth, it was hypothesized that by halting the replacement of shed teeth (which is potentially linked to the reduced exposure to Vitamin D at increased depths), toothlessness occurs quite rapidly. The phenomenon of a downwards migration paired with a colour change to black is also seen in species such as the common fangtooth, although during this process, that species develops fangs for feeding instead of losing them. The apparent rarity of specimens caught during this last stage of life may be a result of the combination of the cessation of feeding and the migration to deeper depths, making them difficult to catch.

References

''Anotopterus pharao''
at

Fishbase FishBase is a global species database of fish species (specifically finfish). It is the largest and most extensively accessed online database on adult finfish on the web.

''Anotopterus pharao''
at the Ichthyoplankton Information System {{Authority control Anotopteridae Taxa named by Erich Zugmayer Fish described in 1911