The smooth lanternshark or slender lanternshark (''Etmopterus pusillus'') is a species of

dogfish shark Squalidae, more commonly known as dogfish, dog sharks, or spiny dogfish, are one of several families of sharks categorized under Squaliformes, making it the second largest order of sharks, numbering 119 species across 7 families. Having earned t ...

in the family Etmopteridae, found widely in the Atlantic and Pacific Oceans. It inhabits

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...

environments at a depth of , and pelagic environments at a depth of . The smooth lanternshark forms a species group with the larger

blurred lanternshark The blurred lanternshark (''Etmopterus bigelowi'') is a little-known species of dogfish shark in the family Etmopteridae, found around the world in benthic and pelagic habitats from a depth of to over down. This shark forms the '' E. pusil ...

(''E. bigelowi''), both of which are distinguished from other members of their family by small, irregularly arranged

dermal denticle A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scales, which can also provide effective camouflage through the use of reflection and colouration, as we ...

s with a truncated shape. This species has a slender, dark brown body with an indistinct black band on the sides over the

pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral surface of fish. The paired pelvic fins are homologous to the hindlimbs of tetrapods. Structure and function Structure In actinopterygians, the pelvic fin consists of two en ...

s, and reaches in length. This slow-growing, ovoviviparous shark feeds on smaller

squid True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting t ...

, fishes, and fish eggs. Smooth lanternsharks are often caught as

bycatch Bycatch (or by-catch), in the fishing industry, is a fish or other marine species that is caught unintentionally while fishing for specific species or sizes of wildlife. Bycatch is either the wrong species, the wrong sex, or is undersized or juve ...

in eastern Atlantic and

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

ese commercial fisheries. The International Union for Conservation of Nature (IUCN) has evaluated this species as of Least Concern because of its wide distribution and limited threats.

Taxonomy and phylogeny

The first

scientific description A species description is a formal description of a newly discovered species, usually in the form of a scientific paper. Its purpose is to give a clear description of a new species of organism and explain how it differs from species that have be ...

of the smooth lanternshark, as ''Acanthidium pusillum'', was published by British biologist Richard Thomas Lowe, in an 1839 issue of the

scientific journal In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research. Content Articles in scientific journals are mostly written by active scientists such as s ...

''Transactions of the Zoological Society of London''. This species was later moved to the genus ''

Etmopterus ''Etmopterus'' is a genus of lantern sharks in the squaliform family Etmopteridae. They are found in deep sea ecosystems of the Atlantic, Indian and Pacific Oceans. Ecology A number of species in this genus function as host to the specialized ...

''. The

specific epithet In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...

''pusillus'' means "weak" in Latin. The smooth lanternshark forms a species group with the

(''E. bigelowi''); these two species are distinguished from other lantern sharks by their irregularly arranged, truncated (ending in a flat crown as though the tip were cut off)

Distribution and habitat

In the Atlantic Ocean, the smooth lanternshark occurs from the Gulf of Mexico to Argentina in the west, Portugal to South Africa (including

Cape Verde , national_anthem = () , official_languages = Portuguese , national_languages = Cape Verdean Creole , capital = Praia , coordinates = , largest_city = capital , demonym ...

and the Azores) in the east, and on the Mid-Atlantic Ridge. In the Indian Ocean, it is found off

KwaZulu-Natal KwaZulu-Natal (, also referred to as KZN and known as "the garden province") is a province of South Africa that was created in 1994 when the Zulu bantustan of KwaZulu ("Place of the Zulu" in Zulu) and Natal Province were merged. It is locate ...

and Madagascar. In the Pacific Ocean, it has been reported from the

East China Sea The East China Sea is an arm of the Western Pacific Ocean, located directly offshore from East China. It covers an area of roughly . The sea’s northern extension between mainland China and the Korean Peninsula is the Yellow Sea, separated b ...

to southern

, in the Hawaiian–Emperor seamount chain area, off

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

and New Zealand, and over the

Nazca Plate The Nazca Plate or Nasca Plate, named after the Nazca region of southern Peru, is an oceanic tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction, along the Peru–Chile Trench, of the Na ...

(including the Amber Seamount and off Isla Salas y Gómez). Smooth lanternsharks are usually found on or near the bottom on continental and insular shelves and slopes at depths of , and possibly to as deep as . Catch data off southern Portugal suggest this species has a preference for rocky substrates, and may conduct a

diel vertical migration Diel vertical migration (DVM), also known as diurnal vertical migration, is a pattern of movement used by some organisms, such as copepods, living in the ocean and in lakes. The word ''diel'' comes from the Latin ''dies'' day, and means a 24-h ...

. In the South Atlantic, this shark also inhabits the open ocean from the surface to a depth of . It has been observed swimming over fields of

hydrothermal vent A hydrothermal vent is a fissure on the seabed from which geothermally heated water discharges. They are commonly found near volcanically active places, areas where tectonic plates are moving apart at mid-ocean ridges, ocean basins, and hotspot ...

Description

Lightly built, the smooth lanternshark has a large head with a pointed snout, large oval eyes, and nostrils with short anterior skin flaps. There are 22–31 tooth rows in the upper jaw and 30–53 tooth rows in the lower jaw. Each upper tooth has a narrow smooth-edged central cusp flanked by 1–2 tiny cusplets; mature males over long grow additional pairs of lateral cusplets with age. The lower teeth are smooth, knife-like, and angled, with their bases interlocking to form a continuous cutting surface. The five pairs of gill slits are long. The first dorsal fin bears a stout spine in front and originates over the free rear tips of the rounded pectoral fins. The second dorsal fin is much larger than the first and has a longer spine. The

s are low and angular, and there is no

anal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

. The caudal fin is short and broad, with a well-developed lower lobe and a ventral notch near the tip of the upper lobe. The skin is covered by many widely spaced, small blocky denticles not arranged in regular rows, giving it a smooth appearance. The coloration is a uniform dark brown, with a faint black mark over the bases of the pelvic fins extending both forward and backward on the flank. The smooth lanternshark is very similar to but smaller than the blurry lanternshark, attaining a length of . The two species differ in a number of anatomical characteristics, but can be most reliably distinguished by the number of turns in their spiral valve

intestine The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The GI tract contains all the major organs of the digestive system, in humans ...

s (10–13 in ''E. pusillus'' versus 16–19 in ''E. bigelowi'').

Biology and ecology

The smooth lanternshark feeds on

, lanternfishes, smaller dogfish sharks, and fish eggs, as well as crustaceans and fish. This species is ovoviviparous, with the developing

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

s being sustained by a yolk sac. Females produce an average of 10 young per reproductive cycle. Males reach sexual maturity at a length of , and females at a length of . The length at maturity varies with geographical region, with sharks in the western Atlantic maturing larger than those from off

. This species grows at a slow rate, with the body becoming relatively longer with age. Off southern Portugal, males live to at least 13 years of age, and females to at least 17 years.

Human interactions

Large numbers of smooth lanternsharks, predominantly juvenile, are caught incidentally by commercial

longline Long line or longline may refer to: *''Long Line'', an album by Peter Wolf *Long line (topology), or Alexandroff line, a topological space *Long line (telecommunications), a transmission line in a long-distance communications network *Longline fish ...

fisheries Fishery can mean either the enterprise of raising or harvesting fish and other aquatic life; or more commonly, the site where such enterprise takes place ( a.k.a. fishing ground). Commercial fisheries include wild fisheries and fish farms, both ...

, and to a lesser extent in bottom trawls and fixed bottom nets, in the eastern Atlantic and off Japan. This species is one of the three most common sharks caught as bycatch in deepwater fisheries off southern Portugal, along with the velvet belly lanternshark (''E. spinax'') and the blackmouth catshark (''Galeus melastomus''). Most captured smooth lanternsharks are discarded, although some may be sold dried and salted for human consumption or processed into fishmeal. The smooth lanternshark's slow rates of reproduction and growth may render it vulnerable to population collapse under sustained fishing pressure. However, catch rates currently show no evidence of this occurring, which, coupled with the smooth lanternshark's wide geographic range, has led to the

IUCN The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

assessing it as of Least Concern. In June 2018 the New Zealand

Department of Conservation An environmental ministry is a national or subnational government agency politically responsible for the environment and/or natural resources. Various other names are commonly used to identify such agencies, such as Ministry of the Environment, ...

classified the smooth lanternshark as "At Risk – Naturally Uncommon" with the qualifiers "Data Poor" and "Secure Overseas" under the

New Zealand Threat Classification System The New Zealand Threat Classification System is used by the Department of Conservation to assess conservation priorities of species in New Zealand. The system was developed because the IUCN Red List, a similar conservation status system, had some ...

References

{{Taxonbar, from=Q957786 Etmopterus Fish described in 1839