Everything about Black Seadevil totally explained
Black seadevils are small, deep-sea
lophiiform fish comprising the
family Melanocetidae. There are five known
species (with only two given
common names), all within the
genus Melanocetus. They are found in tropical to temperate waters of the
Atlantic,
Indian, and
Pacific Ocean, with one species known only from the
Ross Sea.
One of several
anglerfish families, black seadevils are named for their baleful appearance and typically pitch black skin. The family name
Melanocetidae may be translated from the
Greek melanos meaning "black", and
cetus meaning either "
whale" or "
sea monster". The
humpback anglerfish (
Melanocetus johnsonii) was featured on the August
1995 issue of
Time magazine, becoming something of a
flagship species of deep-sea
fauna.
Physical description
Black seadevils are characterised by a gelatinous, mostly
scaleless, globose body; a large head, and generous complement of menacingly large, sharp, glassy fang-like
teeth lining the jaws of a cavernous, oblique mouth. These teeth are depressible and present only in females. In some species there's a scattering of epidermal spinules on the body, and the scales (when present) are conical, hollow, and translucent. Like other anglerfish, black seadevils possess an
illicium and
esca; the former being a modified dorsal
spine—the "
fishing rod"—and the latter being the bulbous,
bioluminescent "
fishing lure". The esca is simple in black seadevils (with either a conical terminus or anterior and posterior ridges in some species) and both it and the illicium are free of
denticles.
The bioluminescence is produced by
symbiotic bacteria; these bacteria are thought to enter the esca via an external duct. (In at least two species, the esca isn't luminous until this duct develops, suggesting the bacteria originate from the surrounding seawater.) The bacteria, belonging to the family
Vibrionaceae, are apparently different in each anglerfish species; the bacteria have yet to be
cultured
in vitro.
The eyes of black seadevils are small; the
pupil is larger than the
lens, leaving an
aphakic space. Common among deep-sea anglerfish is the strong
sexual dimorphism in melanocetids: while females may reach a length of 18 centimetres or more, males remain under 3 centimetres. Aside from jaw teeth, males also lack lures.
Pelvic fins are absent in both sexes. All fins are rounded with slightly incised membranes; the
pectoral fins are small. The single
dorsal fin is positioned far back from the head, larger than and above the retrorse
anal fin.
Females have large, highly distensible stomachs which give the ventral region a flabby appearance. In life, black seadevils are a dark brown to black. The skin is extremely soft and easily abraded during collection or even by simple handling.
Life history
The Melanocetidae appear to buck the trend in deep-sea anglers, in that the males—despite not feeding and thus being little more than couriers of
sperm—are free-living rather than
parasitic. A brief attachment to the female does probably occur, however, as evidenced by a case of mistaken identity: A male humpback anglerfish was found attached to the lip of a female
horned lantern fish (
Centrophryne spinulosa) of an unrelated (though also non-parasitic) family of anglerfish,
Centrophrynidae. Little else is known of their reproduction: They are presumed to be non-guarders, releasing buoyant eggs into the water which become part of the
zooplankton.
While adults have been trawled from as deep as 3,000 metres,
larvae appear to remain in the upper 100 metres of the
water column and gradually descend with maturity. Males likely outnumber—and mature well before—females by a wide margin.
The females use their bioluminescent "fishing poles" to lure both conspecifics and prey, which include
crustaceans and small fish such as
lanternfish and
bristlemouths; the seadevils' highly distensible stomach also allows them to swallow prey larger than themselves, which is an important adaptation to life in the lean depths. In contrast with males, females are poor swimmers and spend most of their time motionless, waiting for something to approach their lures. Predators of black seadevils are not well known, but include
lancetfish.
Species
There are five species in a single genus:
Further Information
Get more info on 'Black Seadevil'.
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