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While many species of the Stomiidae exhibit sexual dimorphism in the form of the size of the body and postorbital photophore, species of the genus Idiacanthus are the most extreme examples. The paedomorphic male is reminiscent of the dwarfted males of the lophiiform suborder Ceratioidei, the deep-sea anglerfishes.
As are most species of the family, I. atlanticus is most likely a diel vertical migrator and predator of other mesopelagic fishes.
As with all members of the genus, Idiacanthus atlanticus is an extremely sexually dimorphic species. Females are extremely elongate, snakelike, with a body depth approximately 2–6% of SL. The head is small, 5–10% of SL. The mouth large, about as long as the head. The upper and lower jaws are armed with barbed, fang-like teeth. The eye is small, on 1–3% of SL. The pectoral fin is absent; the pelvic fin is short and placed at about midbody. A Chin barbel is present, its length about twice the length of the head. The barbel's luminescent tip is laterally compressed and unpigmented. Numerous small photophores cover the head and body. The OA and IC photophores are numerous and closely spaced. The postorbital photophore is much smaller than eye. The skin is smooth, black, and scaleless. The Dorsal-fin origin is anterior to the midpoint of the body, well in advance of the anal-fin origin.
Males are paedomorphic, larval in appearance, and much smaller than females, attaining a maximum size to about 50 mm SL. The barbel is absent and the postorbital photophore is much larger than the orbit. Both the pectoral and pelvic fins are absent.
Meso- to bathypelagic, circumglobal in the Southern hemisphere south of approximately 30°S to the subtropical convergence at depths to 1000 m.
According to the phylogenetic analysis of Fink (1985) and Kenaley (2010), the genus Idiacanthus is sister to Tactostoma. The interrelationships of the species within the genus are unknown.
As with nearly all other members of the Stomiiformes and species of the mesopelagic community, Idiacanthus atlanticus is most likely a diel vertical migrator, making its way to the surface at night to feed.
To about 40 cm SL.
Like nearly all other members of the family stomiidae, Idiacanthus atlanticus is a predator of other mesopelagic fishes, in particular, species of the family Myctophidae (Sutton and Hopkins, 1996).
Idiacanthus atlanticus, the black dragonfish, is a barbeled dragonfish of the family Stomiidae, found circumglobally in southern subtropical and temperate oceans between latitudes 25°S and 60°S, at depths down to 2,000 metres (6,600 ft). The species is sexually dimorphic: females are black with six stripes; males are brown, and lack the females' canine teeth, pelvic fins and barbel. Weigh 13-15 grams. Females are believed to make a diel vertical migration from deeper than 500 metres (1,600 ft) by day to surface waters at night, whereas males do not migrate, remaining below 1,000 metres (3,300 ft) at all times.[2][3]
Length is up to 40 centimetres (16 in) for the female, but only 5 centimetres (2.0 in) for the male. Black dragonfish are bioluminescent, but unlike most such predators, which use their light primarily to attract prey, they can see their own light. As a result, the fish can use their light to hunt. The light is nearly in the infrared and barely visible to the human eye.[4]
In the larval stage, the eyes of the larvae appear as long stalks that dangle out of the body. Eventually, they retreat as the fish ages and reaches maturity.[4]
{{cite web}}: CS1 maint: url-status (link) Idiacanthus atlanticus, the black dragonfish, is a barbeled dragonfish of the family Stomiidae, found circumglobally in southern subtropical and temperate oceans between latitudes 25°S and 60°S, at depths down to 2,000 metres (6,600 ft). The species is sexually dimorphic: females are black with six stripes; males are brown, and lack the females' canine teeth, pelvic fins and barbel. Weigh 13-15 grams. Females are believed to make a diel vertical migration from deeper than 500 metres (1,600 ft) by day to surface waters at night, whereas males do not migrate, remaining below 1,000 metres (3,300 ft) at all times.
Length is up to 40 centimetres (16 in) for the female, but only 5 centimetres (2.0 in) for the male. Black dragonfish are bioluminescent, but unlike most such predators, which use their light primarily to attract prey, they can see their own light. As a result, the fish can use their light to hunt. The light is nearly in the infrared and barely visible to the human eye.
In the larval stage, the eyes of the larvae appear as long stalks that dangle out of the body. Eventually, they retreat as the fish ages and reaches maturity.
