Brown lanternshark
Encyclopedia
The brown lanternshark (Etmopterus unicolor) is a little-known species of deep-sea dogfish shark
in the family Etmopteridae
. It is found off Japan
and New Zealand
, and possibly also South Africa
and Australia
, typically deeper than 300 m (984.3 ft). This species can be distinguished from other lanternsharks by its coloration, which is a uniform dark gray or brown without the ventral surface being much darker and clearly delineated from the rest of the body. The brown lanternshark feeds on small bony fishes, cephalopod
s, and crustacean
s. Reproduction is ovoviviparous, with females giving birth to 9–18 young. An unusually high proportion of individuals in Suruga Bay
are hermaphrodite
s, with both male and female characteristics.
, Japan
. In 1965, Tokiharu Abe redescribed this species and moved it to the genus Etmopterus. The South African Etmopterus compagnoi and the Australian Etmopterus "sp. B" (known as the "bristled lanternshark") are now tentatively believed to be the same as this species. It is grouped with the velvet belly lantern shark
(E. spinax), Caribbean lanternshark
(E. hillianus), fringefin lanternshark
(E. schultzi), broadbanded lanternshark
(E. gracilispinis), combtooth lanternshark
(E. decacuspidatus), and dwarf lanternshark
(E. perryi) in having irregularly arranged, needle-shaped dermal denticles.
, Japan, and around New Zealand. If E. compagnoi and E. sp. B are also considered, then the known range of this species is extended to off South Africa (and possibly southern Namibia
) and southern Australia. The brown lanternshark inhabits continental shelves and seamount
s at a depth of 402–1380 m (1,318.9–4,527.6 ft), though is most common below 900 m (2,952.8 ft). It is generally found deeper than other lanternsharks that share its range, and may have midwater habits.
s are relatively large, about half as long as the eyes. The first dorsal fin
is low with a minute leading spine; the second dorsal fin is twice as high as the first with a much larger spine. The caudal peduncle is short, leading to a long caudal fin with the upper lobe much larger than the lower.
The dermal denticles of this shark are tiny and densely placed with no regular pattern; each denticle has a four-cornered base and rises to a narrow, slightly curved point. The denticles of females are firmly attached, while those of males are easily removed. The coloration is a plain dark gray or brown, slightly darker below and lighter on the dorsal fin margins. Unlike other lanternsharks, there is a not a sharp contrast between the dorsal and ventral colors. There is a horizontal black line on the base of the tail, and another fainter black mark over the pelvic fins. The maximum reported length is 64 cm (25.2 in) for males and 75 cm (29.5 in) for females.
es), followed by cephalopods (mainly the squid
Watasenia scintillans), and finally crustaceans (mainly prawn
s such as Acanthephyra). A known parasite of this shark is a species of copepod
in the genus Lerneopoda.
Like other lanternsharks, the brown lanternshark is ovoviviparous, meaning that the young hatch inside the mother's uterus
and are sustained by a yolk sac
. The litter size is 9–18. Newborns measure 17 cm (6.7 in) in length. Males reach sexual maturity
at a length of 46 cm (18.1 in), and females at a length of 50 cm (19.7 in). A study of brown lanternsharks in Suruga Bay
by Yano and Tanaka (1989) found a 23% prevalence of hermaphroditism within the population. Of the sixteen hermaphrodites examined, fifteen were functional females (and some were pregnant) that also possessed well-developed claspers (male intromittent organ
s), while one was a functional male with ovarian
tissue in the left testis. The reason why so many sharks in Suruga Bay are hermaphroditic is unclear, but has been speculated to relate to pollution
.
Squaliformes
Squaliformes is an order of sharks that includes about 97 species in seven families.Members of the order have two dorsal fins, which usually possess spines, no anal fin or nictitating membrane, and five gill slits. In most other respects, however, they are quite variable in form and size...
in the family Etmopteridae
Etmopteridae
Etmopteridae is a family of sharks in the order Squaliformes, commonly known as lantern sharks. Their name comes from the presence of light-producing photophores on their bodies. The members of this family are small, under long, and are found in deep waters worldwide. There are 45 species in five...
. It is found off Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
and New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, and possibly also South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
and Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, typically deeper than 300 m (984.3 ft). This species can be distinguished from other lanternsharks by its coloration, which is a uniform dark gray or brown without the ventral surface being much darker and clearly delineated from the rest of the body. The brown lanternshark feeds on small bony fishes, cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s, and 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. Reproduction is ovoviviparous, with females giving birth to 9–18 young. An unusually high proportion of individuals in Suruga Bay
Suruga Bay
Suruga Bay is a bay on the Pacific coast of Honshū in Shizuoka Prefecture, Japan. It is situated north of an imaginary line joining Omaezaki Point and Irōzaki Point at the tip of the Izu Peninsula and surrounded by Honshū to the southwest and west and the Izu Peninsula to the east.-Geology:Suruga...
are hermaphrodite
Hermaphrodite
In biology, a hermaphrodite is an organism that has reproductive organs normally associated with both male and female sexes.Many taxonomic groups of animals do not have separate sexes. In these groups, hermaphroditism is a normal condition, enabling a form of sexual reproduction in which both...
s, with both male and female characteristics.
Taxonomy
The brown lanternshark was first described by Robert Engelhardt as Spinax unicolor in 1912, in the scientific journal Zoologischer Anzeiger. The type specimen was a 55 cm (21.7 in) long female from Sagami BaySagami Bay
Sagami Bay , also known as the Sagami Gulf or Sagami Sea, lies south of Kanagawa Prefecture in Honshū, central Japan, contained within the scope of the Miura Peninsula, in Kanagawa, to the east, the Izu Peninsula, in Shizuoka Prefecture, to the west, and the Shōnan coastline to the north, while the...
, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
. In 1965, Tokiharu Abe redescribed this species and moved it to the genus Etmopterus. The South African Etmopterus compagnoi and the Australian Etmopterus "sp. B" (known as the "bristled lanternshark") are now tentatively believed to be the same as this species. It is grouped with the velvet belly lantern shark
Velvet belly lantern shark
The velvet belly lantern shark is a species of dogfish shark in the family Etmopteridae. One of the most common deepwater sharks in the northeastern Atlantic Ocean, the velvet belly is found from Iceland and Norway to Gabon and South Africa at a depth of...
(E. spinax), Caribbean lanternshark
Caribbean lanternshark
The Caribbean lanternshark, Etmopterus hillianus, is a shark of the family Etmopteridae found in the eastern and western Atlantic at depths of between 180 and 720 m. Its length is up to 50 cm.Reproduction is ovoviviparous.-References:...
(E. hillianus), fringefin lanternshark
Fringefin lanternshark
The fringefin lanternshark, Etmopterus schultzi, is a shark of the family Etmopteridae found in the western central Atlantic from Texas to Florida, northern Gulf of Mexico, and Mexico.-References:...
(E. schultzi), broadbanded lanternshark
Broadbanded lanternshark
The broadbanded lanternshark, Etmopterus gracilispinis, is a shark of the family Etmopteridae found in the western and southeast Atlantic, between latitudes 40°N and 45°S, at depths of between 70 and 1,000 m...
(E. gracilispinis), combtooth lanternshark
Combtooth lanternshark
The combtoothed lanternshark, Etmopterus decacuspidatus, is a shark of the family Etmopteridae the only specimen, and holotype, being found from the South China Sea between the Viet Nam coast and Hainan Island, at a depth of between 510 and 690 m...
(E. decacuspidatus), and dwarf lanternshark
Dwarf lanternshark
The dwarf lanternshark is a little-known species of dogfish shark in the family Etmopteridae and possibly the smallest shark in the world, reaching a maximum known length of . It is known to be present only on the upper continental slopes off Colombia and Venezuela, at a depth of...
(E. perryi) in having irregularly arranged, needle-shaped dermal denticles.
Distribution and habitat
Confirmed specimens of the brown lanternshark have been captured from off southern HonshuHonshu
is the largest island of Japan. The nation's main island, it is south of Hokkaido across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyushu across the Kanmon Strait...
, Japan, and around New Zealand. If E. compagnoi and E. sp. B are also considered, then the known range of this species is extended to off South Africa (and possibly southern Namibia
Namibia
Namibia, officially the Republic of Namibia , is a country in southern Africa whose western border is the Atlantic Ocean. It shares land borders with Angola and Zambia to the north, Botswana to the east and South Africa to the south and east. It gained independence from South Africa on 21 March...
) and southern Australia. The brown lanternshark inhabits continental shelves and seamount
Seamount
A seamount is a mountain rising from the ocean seafloor that does not reach to the water's surface , and thus is not an island. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from a seafloor of depth. They are defined by oceanographers as...
s at a depth of 402–1380 m (1,318.9–4,527.6 ft), though is most common below 900 m (2,952.8 ft). It is generally found deeper than other lanternsharks that share its range, and may have midwater habits.
Description
The brown lanternshark has a robust, almost cylindrical body with a wide, flattened head. There are around 28 tooth rows in the upper jaw and 34 tooth rows in the lower jaw. The upper teeth have a pointed central cusp flanked by fewer than three pairs of lateral cusplets, while the bottom teeth are large and tipped with a strongly angled triangular cusp. The five pairs of gill slitGill slit
Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of Cartilaginous fish such as sharks, rays, sawfish, and guitarfish. Most of these have five pairs, but a few species have 6 or 7 pairs...
s are relatively large, about half as long as the eyes. The first 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 low with a minute leading spine; the second dorsal fin is twice as high as the first with a much larger spine. The caudal peduncle is short, leading to a long caudal fin with the upper lobe much larger than the lower.
The dermal denticles of this shark are tiny and densely placed with no regular pattern; each denticle has a four-cornered base and rises to a narrow, slightly curved point. The denticles of females are firmly attached, while those of males are easily removed. The coloration is a plain dark gray or brown, slightly darker below and lighter on the dorsal fin margins. Unlike other lanternsharks, there is a not a sharp contrast between the dorsal and ventral colors. There is a horizontal black line on the base of the tail, and another fainter black mark over the pelvic fins. The maximum reported length is 64 cm (25.2 in) for males and 75 cm (29.5 in) for females.
Biology and ecology
The most important prey of the brown lanternshark are bony fishes (mainly lanternfishLanternfish
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...
es), followed by cephalopods (mainly the squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
Watasenia scintillans), and finally crustaceans (mainly prawn
Prawn
Prawns are decapod crustaceans of the sub-order Dendrobranchiata. There are 540 extant species, in seven families, and a fossil record extending back to the Devonian...
s such as Acanthephyra). A known parasite of this shark is a species of copepod
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
in the genus Lerneopoda.
Like other lanternsharks, the brown lanternshark is ovoviviparous, meaning that the young hatch inside the mother's uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
and are sustained by a yolk sac
Yolk sac
The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...
. The litter size is 9–18. Newborns measure 17 cm (6.7 in) in length. Males reach sexual maturity
Sexual maturity
Sexual maturity is the age or stage when an organism can reproduce. It is sometimes considered synonymous with adulthood, though the two are distinct...
at a length of 46 cm (18.1 in), and females at a length of 50 cm (19.7 in). A study of brown lanternsharks in Suruga Bay
Suruga Bay
Suruga Bay is a bay on the Pacific coast of Honshū in Shizuoka Prefecture, Japan. It is situated north of an imaginary line joining Omaezaki Point and Irōzaki Point at the tip of the Izu Peninsula and surrounded by Honshū to the southwest and west and the Izu Peninsula to the east.-Geology:Suruga...
by Yano and Tanaka (1989) found a 23% prevalence of hermaphroditism within the population. Of the sixteen hermaphrodites examined, fifteen were functional females (and some were pregnant) that also possessed well-developed claspers (male intromittent organ
Intromittent organ
An intromittent organ is a general term for an external organ of a male organism that is specialized to deliver sperm during copulation. Intromittent organs are found most often in terrestrial species, as most aquatic species fertilize their eggs externally, although there are...
s), while one was a functional male with ovarian
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
tissue in the left testis. The reason why so many sharks in Suruga Bay are hermaphroditic is unclear, but has been speculated to relate to pollution
Pollution
Pollution is the introduction of contaminants into a natural environment that causes instability, disorder, harm or discomfort to the ecosystem i.e. physical systems or living organisms. Pollution can take the form of chemical substances or energy, such as noise, heat or light...
.