Overview

Brief Summary

Introduction

The family Melanocetidae includes globose bathypelagic anglerfishes, easily separated from members of allied families by having a combination of features that includes 12 or more dorsal-fin rays, three to five anal-fin rays, a huge mouth, and numerous long fang-like teeth (Bertelsen, 1951; Pietsch, 1972a; Pietsch and Van Duzer, 1980). The only currently recognized genus of the family was established by Günther (1864) with the description of Melanocetus johnsonii, based on a single female specimen collected in the Atlantic Ocean off Madeira. Since that time, 13 additional species based on females have been described. The family currently includes six recognized species (Pietsch and Van Duzer,1980; Balushkin and Fedorov, 1981)

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Comprehensive Description

Characteristics

Diagnosis

Metamorphosed males and females of the family Melanocetidae are distinguished from those of all other ceratioid families by having a combination of 13-16 (rarely 12 or 17) dorsal-fin rays and 4 (rarely 3 or 5) anal-fin rays.

Metamorphosed females are further differentiated by having the following combination of character states: supraethmoid present; frontals widely separated, each with a prominent ventromedial extension; parietals present; sphenotic spines absent; pterosphenoid, metapterygoid, and mesopterygoid present; hyomandibular with a double head; hypohyals 2; branchiostegal rays 6 (2 , 4); opercle bifurcate, dorsal fork reduced; subopercle long and slender, as long as lower fork of opercle in some specimens, ventral part with a well-developed spine on anterior margin; quadrate, articular, angular, and preopercular spines absent; jaws equal anteriorly; lower jaw with a well-developed symphysial spine; postmaxillary process of premaxilla absent; anterior-maxillomandibular ligament absent; pharyngobranchials I and IV absent; pharyngobranchials II and III well developed and toothed; epibranchial I reduced; hypobranchials I-III well developed; a single ossified basibranchial; epibranchial and ceratobranchial teeth absent; epibranchial I and proximal one-half of ceratobranchial I bound to wall of pharynx by connective tissue; distal end of ceratobranchial I free, not bound by connective tissue to adjacent ceratobranchial II; proximal one-quarter to one-half of ceratobranchials II-IV not bound together by connective tissue; epurals absent; hypural plate entire, without posterior notch; pterygiophore of illicium bearing a small ossified remnant of second cephalic spine; escal bulb and central lumen present, esca without tooth-like denticles; posteroventral process of coracoid absent; pectoral radials 4, fusing to 3 with growth; pelvic bones expanded distally; pectoral-fin rays 15-23; pelvic fins absent; caudal-fin rays 9 (1 simple, 6 bifurcated, 2 simple); skin with minute widely spaced dermal spinules in at least some specimens (only visible microscopically in cleared and stained material; see Pietsch and Van Duzer, 1980:67); ovaries paired; pyloric caecae absent.

Free-living male of Melanocetus sp, ZMUC P92675. After Bertelsen (1951). © 1951, 1983 Bertelsen

Metamorphosed males are further differentiated in having the following combination of character states: eyes directed laterally, elliptical in shape, pupil larger than lens; olfactory organs large, nostrils lateral, inflated; nasal area unpigmented; 12-24 olfactory lamellae; jaw teeth absent; upper denticular with 2 or 3 semicircular series of strong recurved denticles, fused with a median series of 3-9 enlarged dermal spines that articulate with the pterygiophore of the illicium; lower denticular with 10-23 recurved denticles, fused into a median and two lateral groups; skin spinulose or naked; fin-ray counts as given for metamorphosed females; free-living, never parasitic, two known examples of males attached to females in temporary coupling (Pietsch, 2005).

Larvae are further differentiated in having the following combination of character states: body short, almost spherical; skin moderately inflated; pectoral fins of normal size, not reaching beyond dorsal and anal fins; pelvic fins absent; sexual dimorphism evident, females with a small, club-shaped illicial rudiment protruding from head; fin-ray counts as given for metamorphosed females; metamorphosis beginning at lengths of 8-10 mm SL (Bertelsen, 1951:45, 49, figs. 16A-G, 17A-F; 1984:326, 328, fig. 169C-D).

Description

Metamorphosed females with body short and deep, globular, depth 60-75% SL (but often appearing highly compressed due apparently to deformation following capture); head short; mouth large, opening oblique to nearly vertical, cleft not extending past eye; jaws equal anteriorly; oral valve weakly developed; two nostrils on each side on distal surface of a rounded papilla; eye small, subcutaneous, appearing through a circular translucent area of integument within a shallow orbital pit formed between sphenotic and frontal bones; teeth slender, recurved, and depressible, some slightly hooked distally, those in lower jaw less numerous (except in some small specimens, less than approximately 20 mm SL) but slightly longer than those in upper jaw; number of teeth in upper jaw 29-178, in lower jaw 32-142; longest tooth in lower jaw 6.9-25.0% SL; number of vomerine teeth 0-12; epibranchial I bound to wall of pharynx; epibranchials I-IV closely bound together; proximal one-half of ceratobranchial I bound to wall of pharynx, distal half free; epibranchial IV and ceratobranchial IV bound to wall of pharynx, no opening behind fourth arch; gill filaments absent on epibranchials, present on proximal tip of ceratobranchial I and full length of ceratobranchials II-IV; pseudobranch absent; length of illicium 23.1-60.8% SL; anteriormost tip of pterygiophore of illicium exposed, emerging on snout between eyes, posterior end concealed under skin; escal bulb simple, usually with a rounded or conical distal prolongation, and often with posterior and anterior crests; elongate escal appendages and filaments absent; neuromasts of acoustico-lateralis system located at tips of low cutaneous papillae, pattern of placement as described for other ceratioids (Pietsch, 1969, 1972b, 1974a, 1974b).

Color of metamorphosed females dark brown to black over entire surface of head and body (except for distal portion of escal bulb) and oral cavity; all fins white in specimens less than approximately 40 mm (except for caudal-fin rays of adolescent specimens of Melanocetus murrayi; Bertelsen, 1951:47, fig. 16I). Metamorphosed males with outer pigmentation as for females (except nasal area unpigmented), subdermal pigmentation variable (Bertelsen, 1951:42; Pietsch and Van Duzer, 1980:83).

The largest known female is a 135-mm specimen of M. johnsonii; the largest known metamorphosed male, also identified as M. johnsoni, measures 28 mm.

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Distribution

Melanocetus johnsonii and M. murrayi, by far the best known species of the genus, have broad distributions, the former known from all three major oceans of the world, the latter from the Atlantic and Pacific. Melanocetus rossi is represented by a single specimen collected in the Ross Sea, Antarctica; M. polyactis and M. niger, known from 15 and six specimens, respectively, are both restricted to the eastern tropical Pacific; and M. eustales, is known from a single specimen collected in the eastern Pacific off Mazatlán, Mexico.

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Ecology

Habitat

Depth range based on 108 specimens in 4 taxa.
Water temperature and chemistry ranges based on 96 samples.

Environmental ranges
  Depth range (m): 0 - 4300
  Temperature range (°C): 1.785 - 22.540
  Nitrate (umol/L): 0.259 - 44.278
  Salinity (PPS): 33.836 - 36.586
  Oxygen (ml/l): 0.217 - 7.011
  Phosphate (umol/l): 0.042 - 3.220
  Silicate (umol/l): 0.921 - 163.066

Graphical representation

Depth range (m): 0 - 4300

Temperature range (°C): 1.785 - 22.540

Nitrate (umol/L): 0.259 - 44.278

Salinity (PPS): 33.836 - 36.586

Oxygen (ml/l): 0.217 - 7.011

Phosphate (umol/l): 0.042 - 3.220

Silicate (umol/l): 0.921 - 163.066
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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Evolution and Systematics

Evolution

Discussion of Phylogenetic Relationships

View Melanocetus Tree

The Melanocetidae appears to be a relatively primitive ceratioid family (Bertelsen 1951; Pietsch 1972a, 1976, 1979). The five species are characterized by a confusing mosaic of primitive and derived character states such that an interpretation of interspecific phylogenetic relationships is difficult. In any case, however, it seems apparent that M. murrayi has split off from the main line of melanocetid evolution and acquired a number of unique features that reflect its most derived position in the genus: 1) depressed cranium, 2) concave vomer, 3) small pectoral fin, 4) tiny escal bulb, and 5) thin integument. Living in considerably deeper strata than its congeners most probably also reflects a derived condition.

The four remaining species are much more closely related to each other than any is to M. murrayi. Five characters can be used to distinguish these forms: 1) number of lower jaw teeth, 2) longest lower jaw tooth, 3) illicium length, 4) escal bulb width, and 5) escal morphology. Unfortunately, all but the last of these characters overlap in variation among the remaining forms of the genus, and, furthermore, the relative primitiveness of character states among these features is nearly impossible to determine. Melanocetus johnsonii is perhaps derived in having a relatively long illicium, and in having fewer, but longer jaw teeth (see Pietsch 1972b, 1974a). Melanocetus polyactis and M. niger are similar in having relatively short jaw teeth, a similar escal morphology lacking anterior and posterior crests, and a sympatric geographic distribution that is restricted to the Gulf of Panama and adjacent eastern tropical Pacific. Melanocetus eustalus is derived in having an extremely large escal bulb, comparable to no other known ceratioid.

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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
                                        
Specimen Records:39Public Records:8
Specimens with Sequences:32Public Species:3
Specimens with Barcodes:30Public BINs:2
Species:4         
Species With Barcodes:4         
          
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Source: Barcode of Life Data Systems (BOLD)

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Barcode data

Creative Commons Attribution 3.0 (CC BY 3.0)

© Barcode of Life Data Systems

Source: Barcode of Life Data Systems (BOLD)

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Locations of barcode samples

Collection Sites: world map showing specimen collection locations for Melanocetus

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Source: Barcode of Life Data Systems (BOLD)

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Wikipedia

Black seadevil

Black seadevils are small, deepsea lophiiform fishes of the family Melanocetidae. The five known species (with only two given common names) are all within the genus Melanocetus. They are found in tropical to temperate waters of the Atlantic, Indian, and Pacific Oceans, 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 14, 1995, issue of Time magazine,[1] becoming something of a flagship species of deepsea fauna.

Species[edit]

The currently recognized species in this genus are: [2]

Physical description[edit]

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. Some species have a scattering of epidermal spinules on the body, and the scales (when present) are conical, hollow, and translucent. Like other anglerfishes, 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 is not 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 deepsea anglerfish is the strong sexual dimorphism in melanocetids: while females may reach a length of 18 cm (7 in) or more, males remain under 3 cm (1 in). 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.

Humpback anglerfish

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[edit]

The Melanocetidae appear to buck the trend in deepsea 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 nonparasitic) family of anglerfish, Centrophrynidae. Little else is known of their reproduction: They are presumed to not be guarders, releasing buoyant eggs into the water which become part of the zooplankton.

While adults have been trawled from as deep as 3,000 m (9,900 ft), larvae appear to remain in the upper 100 m (330 ft) 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 stomachs also allow 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.

References[edit]

  1. ^ Cover of the August 14 issue of Time.
  2. ^ Froese, Rainer, and Daniel Pauly, eds. (2012). Species of Melanocetus in FishBase. April 2012 version.
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