Gigantactis


Gigantactis is a genus of marine ray-finned fish belonging to the family Gigantactinidae, the whipnose anglers. The fishes in this genus have a circumglobal distribution in the deep waters of the tropical and temperate zones of the Atlantic, Indian and Pacific Oceans.

Taxonomy

Gigantactis was first proposed as a monospecific genus in 1902 by the German zoologist August Brauer when he described Gigantactis vanhoeffeni. The type locality of G. vanhoeffeni was given as the Indian Ocean east of Zanzibar from Valdivia station 239 from the surface to a depth of. This genus was classified in the monotypic family Gigantactinidae in 1904 by the Belgian-born British ichthyologist George Albert Boulenger, with a second genus, Rhynchactis, being added by the English ichthyologist Charles Tate Regan in 1925. The fifth edition of Fishes of the World classifies the whipnose anglers within the suborder Certioidei within the order Lophiiformes, the anglerfishes.

Etymology

Giganactis is a combination of gigantos, meaning "giant", with actis, which means "ray", an allusion to the unusually long illicium of genus's type species, G. vanhoeffeni.

Species

Giganactis contains 22 recognized extant species:Gigantactis balushkini Kharin, 1984Gigantactis cheni H. C. Ho & K. T. Shao, 2019Gigantactis elsmani Bertelsen, Pietsch III|Pietsch] & Lavenberg, 1981 Gigantactis gargantua Bertelsen, Pietsch & Lavenberg, 1981 Gigantactis gibbsi Bertelsen, Pietsch & Lavenberg, 1981Gigantactis golovani Bertelsen, Pietsch & Lavenberg, 1981Gigantactis gracilicauda Regan, 1925Gigantactis herwigi Bertelsen, Pietsch & Lavenberg, 1981Gigantactis ios Bertelsen, Pietsch & Lavenberg, 1981Gigantactis kreffti Bertelsen, Pietsch & Lavenberg, 1981Gigantactis longicauda Bertelsen & Pietsch, 2002Gigantactis longicirra Waterman, 1939Gigantactis macronema Regan, 1925Gigantactis meadi Bertelsen, Pietsch & Lavenberg 1981 Gigantactis microdontis Bertelsen, Pietsch & Lavenberg, 1981 Gigantactis microphthalmus Regan & Trewavas, 1932

Characteristics

Gigantactis whipnose anglers are distinguished from the other genus in the family, Rhynchactis, by the absence of pelvic bones and by the possession of between 5 and 9 rays, rarely 4 or 10, in the dorsal fin and the anal fin containing between 5 and 7, rarely 4 or 8, soft rays. In the metamorphosed females, the possession of frontal bones, parietal bones with teeth along their full lengths. The maxilla is reduced to a thread-like remnant, and the dentary has several rows of robust, recurved teeth. They have a single hypohyal and spiny skin. The illicium originates on the tip of the snout, the snout being in front of the mouth, with the esca at its tip bearing a bioluminescent organ. The metamorphosed males have larger eyes than those of Rhynchactis, typically having 12 olfactory lamellae, deep nostrils with a depth greater than 9% of the standard length. They normally have 3 upper denticular teeth and 4 lower denticular teeth, all separate from each other. The skin may be either pigmented or unpigmented and may be naked or covered in spinules. The largest species in the genus is G. vanhoeffeni with a maximum published total length of.

Distribution and habitat

Gigantactis has a circumglobal distribution in the Atlantic, Indian and Pacific Oceans. They are found at depths between the surface and.

Feeding mechanism

Gigantactis have a very long illicium that is not as mobile as the illicia of other Ceratioid taxa and is vibrated rather than waved; the vibration and bioluminescence of the esca lure the prey. The mouth is used to trap prey in a cage made by the long recurved teeth, which is similar to the wolftrap anglers although, in this genus, the teeth grow from the lower jaw rather than the upper jaw. It is not known how the prey is detected, but the esca and illicium appear to be sensitive and may detect the prey or the pressure waves caused by the prey; the fish then lunges to the prey in its mouth. The prey is then processed by the pharyngeal teeth. Very few specimens have prey in their stomachs when caught, mainly cephalopods with one copepod found.

Reproduction

Gigantactis males are relatively large. They only temporarily attach to much larger females with their pincer-like denticles.