Black seadevils are small, deep-sea lophiiform fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

 comprising the family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 Melanocetidae. There are five known species

Species

In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 (with only two given common name

Common name

A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...

s), all within the genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Melanocetus. They are found in tropical to temperate waters of the Atlantic

Atlantic Ocean

The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

, Indian

Indian Ocean

The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...

, and Pacific Ocean

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

, with one species known only from the Ross Sea

Ross Sea

The Ross Sea is a deep bay of the Southern Ocean in Antarctica between Victoria Land and Marie Byrd Land.-Description:The Ross Sea was discovered by James Ross in 1841. In the west of the Ross Sea is Ross Island with the Mt. Erebus volcano, in the east Roosevelt Island. The southern part is covered...

.

One of several anglerfish

Anglerfish

Anglerfishes are members of the teleost order Lophiiformes . They are bony fishes named for their characteristic mode of predation, wherein a fleshy growth from the fish's head acts as a lure; this is considered analogous to angling.Some anglerfishes are pelagic , while others are benthic...

 families, black seadevils are named for their baleful appearance and typically pitch black skin. The family name Melanocetidae may be translated from the Greek

Greek language

Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 melanos meaning "black", and cetus meaning either "whale

Whale

Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...

" or "sea monster

Sea monster

Sea monsters are sea-dwelling mythical or legendary creatures, often believed to be of immense size.Marine monsters can take many forms, including sea dragons, sea serpents, or multi-armed beasts. They can be slimy or scaly and are often pictured threatening ships or spouting jets of water...

". The humpback anglerfish

Humpback anglerfish

The humpback anglerfish or common black devil, Melanocetus johnsonii, is a deep-sea anglerfish in the family Melanocetidae, found in tropical to temperate parts of all oceans at depths of up to 2,000 meters...

 (Melanocetus johnsonii) was featured on the August 1995 issue of Time magazine, becoming something of a flagship species

Flagship species

The concept of flagship species is a surrogate species concept with its genesis in the field of conservation biology. The flagship species concept holds that by raising the profile of a particular species, it can successfully leverage more support for biodiversity conservation at large in a...

 of deep-sea fauna

Fauna

Fauna or faunæ is all of the animal life of any particular region or time. The corresponding term for plants is flora.Zoologists and paleontologists use fauna to refer to a typical collection of animals found in a specific time or place, e.g. the "Sonoran Desert fauna" or the "Burgess shale fauna"...

.

Physical description

Black seadevils are characterised by a gelatinous, mostly scaleless

Scale (zoology)

In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...

, globose body; a large head, and generous complement of menacingly large, sharp, glassy fang-like teeth

Tooth

Teeth are small, calcified, whitish structures found in the jaws of many vertebrates that are used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are embedded in the Mandible bone or the Maxillary bone and are...

 lining the jaws of a cavernous, oblique mouth. These teeth are depressible and present only in females. In some species there is 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

Illicium

Illicium is a genus of flowering plants containing 42 species of evergreen shrubs and small trees, in family Schisandraceae. The species are native to the tropical and subtropical regions of eastern and southeastern Asia, southeastern North America, and the West Indies.Selected species*Illicium...

and esca; the former being a modified dorsal spine

Vertebral column

In human anatomy, the vertebral column is a column usually consisting of 24 articulating vertebrae, and 9 fused vertebrae in the sacrum and the coccyx. It is situated in the dorsal aspect of the torso, separated by intervertebral discs...

—the "fishing rod

Fishing rod

A fishing rod or a fishing pole is a tool used to catch fish, usually in conjunction with the pastime of angling, and can also be used in competition casting. . A length of fishing line is attached to a long, flexible rod or pole: one end terminates in a hook for catching the fish...

"—and the latter being the bulbous, bioluminescent

Bioluminescence

Bioluminescence is the production and emission of light by a living organism. Its name is a hybrid word, originating from the Greek bios for "living" and the Latin lumen "light". Bioluminescence is a naturally occurring form of chemiluminescence where energy is released by a chemical reaction in...

 "fishing lure

Fishing lure

A fishing lure is an object attached to the end of a fishing line which is designed to resemble and move like the prey of a fish. The purpose of the lure is to use movement, vibration, and colour to catch the fish's attention so it bites the hook...

". 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

Symbiosis

Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...

 bacteria; these bacteria are thought to enter the esca via an external duct. (In at least two species, the esca is not luminous until this duct develops, suggesting the bacteria originate from the surrounding seawater.) The bacteria, belonging to the family Vibrionaceae

Vibrionaceae

The Vibrionaceae are a family of Proteobacteria, given their own order. Inhabitants of fresh or salt water, several species are pathogenic, including the type species Vibrio cholerae, which is the agent responsible for cholera...

, are apparently different in each anglerfish species; the bacteria have yet to be culture

Microbiological culture

A microbiological culture, or microbial culture, is a method of multiplying microbial organisms by letting them reproduce in predetermined culture media under controlled laboratory conditions. Microbial cultures are used to determine the type of organism, its abundance in the sample being tested,...

d in vitro

In vitro

In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...

.

The eyes of black seadevils are small; the pupil

Pupil

The pupil is a hole located in the center of the iris of the eye that allows light to enter the retina. It appears black because most of the light entering the pupil is absorbed by the tissues inside the eye. In humans the pupil is round, but other species, such as some cats, have slit pupils. In...

 is larger than the lens

Lens (anatomy)

The crystalline lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to be focused on the retina. The lens, by changing shape, functions to change the focal distance of the eye so that it can focus on objects at various distances, thus allowing a...

, leaving an aphakic

Aphakia

Aphakia is the absence of the lens of the eye, due to surgical removal, a perforating wound or ulcer, or congenital anomaly. It causes a loss of accommodation, hyperopia, and a deep anterior chamber. Complications include detachment of the vitreous or retina, and glaucoma.Aphakic people are...

 space. Common among deep-sea anglerfish is the strong sexual dimorphism

Sexual dimorphism

Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...

 in melanocetids: while females may reach a length of 18 centimetres (7 inches) or more, males remain under 3 centimetres (1 inch). 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

Dorsal fin

A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...

 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

Spermatozoon

A spermatozoon is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote...

—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

Horned lantern fish

The horned lantern fish or prickly seadevil, Centrophryne spinulosa, is a deep-sea anglerfish found worldwide. It is the sole species in the family Centrophrynidae, distinguished from other deep-sea anglerfishes by various characters including four pectoral radials, an anterior spine on the...

 (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

Zooplankton

Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...

.

While adults have been trawled from as deep as 3,000 metres (9,900 feet), larva

Larva

A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

e appear to remain in the upper 100 metres (330 feet) 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 crustacean

Crustacean

Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...

s and small fish such as lanternfish

Lanternfish

Cooper Lanternfishes are small mesopelagic fish of the large family Myctophidae. One of two families in the order Myctophiformes, the Myctophidae are represented by 246 species in 33 genera, and are found in oceans worldwide. They are aptly named after their conspicuous use of bioluminescence...

 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

Lancetfish

Lancetfishes are large oceanic predatory fishes in the genus Alepisaurus , the only living genus in the family Alepisauridae....

.

Species

There are five species in a single genus:

• Melanocetus eustalus Pietsch & Van Duzer, 1980.
• Humpback anglerfish
  Humpback anglerfish
  The humpback anglerfish or common black devil, Melanocetus johnsonii, is a deep-sea anglerfish in the family Melanocetidae, found in tropical to temperate parts of all oceans at depths of up to 2,000 meters...
  
  , Melanocetus johnsonii Günther, 1864.
• Murray's abyssal anglerfish, Melanocetus murrayi Günther, 1887.
• Melanocetus niger Regan, 1925.
• Melanocetus rossi Balushkin & Fedorov, 1981.