Longnose pygmy shark
Encyclopedia
The longnose pygmy shark (Heteroscymnoides marleyi) is a rare species
of dogfish shark
in the family
Dalatiidae
and the only member
its genus
. It is known only from a handful of specimens collected from the cold oceanic
waters of the Southern Hemisphere
, between the surface and a depth of 502 m (1,647 ft). Reaching 37 cm (14.6 in) in length, this diminutive shark is characterized by a slender, dark brown body with a very long, bulbous snout. In addition, it has two spineless dorsal fin
s of nearly equal size, with the origin of the first lying over the pectoral fin bases. The longnose pygmy shark does not appear substantially threatened by fisheries, and has been assessed as Least Concern
by the International Union for Conservation of Nature (IUCN).
in a 1934 volume of Proceedings of the Academy of Natural Sciences of Philadelphia, based on a 13 cm (5.1 in) long female collected off Point Ocean Beach in Durban
, South Africa
. Fowler had originally thought the shark to belong to the genus Heteroscymnus (a junior synonym of Somniosus
), and thus he created for it the new genus Heteroscymnoides from the Greek
oidos ("resemblance"). He gave it the specific epithet marleyi in honor of Harold Walter Bell-Marley, and his contributions to the study of South African fishes. The relationship between Heteroscymnoides and the rest of its family is uncertain.
off eastern KwaZulu-Natal
, in the southeastern Atlantic Ocean
near the Walvis Ridge
, and in the southwestern Pacific Ocean
off Chile
. These records suggest that it may have a circumglobal distribution in the Southern Hemisphere
, inhabiting subantarctic
waters and cold ocean current
s, including the Benguela
and the Humboldt
. This species occurs in the open ocean between the surface and a depth of 502 m (1,647 ft), in water 830–4000 m (2,723.1–13,123.4 ft) deep.
s (protective third eyelids), and are followed by large spiracle
s. The nostrils are long and angled, with a very short flap of skin on their anterior rims. The mouth is transverse and surrounded by thin, smooth lips. The upper teeth number 22 rows and are small and upright with a single narrow cusp. The lower teeth number 23 rows and are much larger, broader, and knife-like, and interlock to form a continuous cutting surface. The five pairs of gill slit
s are tiny and of uniform width.
The two dorsal fin
s lack spines. The first dorsal originates over the pectoral fin bases; the second dorsal is slightly larger than the first but is about equal in base length, and originates over the middle of the pelvic fin bases. The pectoral fins are short and somewhat paddle-like. There is no anal fin. The caudal fin is broad, with a well-developed lower lobe and a deep ventral notch near the tip of the upper lobe. The small dermal denticles have sharp wedge-shaped crowns bearing median ridges, and are placed on stalks (pedicels). This species is dark brown, with prominent blackish, then light bands at the fin margins. The underside is covered by minute light-producing photophore
s.
s, and is presumably aplacental viviparous with a small litter size like other members of its family. The 13 cm (5.1 in) long type specimen had an umbilical scar, suggesting that it was close to the birth size. Males and females attain sexual maturity
at under 36 and 33 cm (14.2 and 13 in) long respectively.
by the International Union for Conservation of Nature (IUCN).
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...
of dogfish shark
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
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...
Dalatiidae
Dalatiidae
Dalatiidae is a family of sharks in the order Squaliformes, commonly known as kitefin sharks . Members of this family are small, under long, and are found worldwide. They have cigar-shaped bodies with narrow heads and rounded snouts...
and the only member
Monotypic
In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...
its 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...
. It is known only from a handful of specimens collected from the cold oceanic
Pelagic zone
Any water in a sea or lake that is not close to the bottom or near to the shore can be said to be in the pelagic zone. The word pelagic comes from the Greek πέλαγος or pélagos, which means "open sea". The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes...
waters of the Southern Hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...
, between the surface and a depth of 502 m (1,647 ft). Reaching 37 cm (14.6 in) in length, this diminutive shark is characterized by a slender, dark brown body with a very long, bulbous snout. In addition, it has two spineless 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...
s of nearly equal size, with the origin of the first lying over the pectoral fin bases. The longnose pygmy shark does not appear substantially threatened by fisheries, and has been assessed as Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
by the International Union for Conservation of Nature (IUCN).
Taxonomy
The longnose pygmy shark was described by American zoologist Henry Weed FowlerHenry Weed Fowler
Henry Weed Fowler was an American zoologist born in Holmesburg, Pennsylvania.He studied at Stanford University under David Starr Jordan...
in a 1934 volume of Proceedings of the Academy of Natural Sciences of Philadelphia, based on a 13 cm (5.1 in) long female collected off Point Ocean Beach in Durban
Durban
Durban is the largest city in the South African province of KwaZulu-Natal and the third largest city in South Africa. It forms part of the eThekwini metropolitan municipality. Durban is famous for being the busiest port in South Africa. It is also seen as one of the major centres of tourism...
, 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...
. Fowler had originally thought the shark to belong to the genus Heteroscymnus (a junior synonym of Somniosus
Somniosus
Somniosus is a genus of dogfish sharks in the family Somniosidae.-Species:* Somniosus microcephalus * Somniosus pacificus Bigelow & Schroeder, 1944...
), and thus he created for it the new genus Heteroscymnoides 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;...
oidos ("resemblance"). He gave it the specific epithet marleyi in honor of Harold Walter Bell-Marley, and his contributions to the study of South African fishes. The relationship between Heteroscymnoides and the rest of its family is uncertain.
Distribution and habitat
The longnose pygmy shark has been caught in the western Indian OceanIndian 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...
off eastern KwaZulu-Natal
KwaZulu-Natal
KwaZulu-Natal is a province of South Africa. Prior to 1994, the territory now known as KwaZulu-Natal was made up of the province of Natal and the homeland of KwaZulu....
, in the southeastern Atlantic Ocean
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...
near the Walvis Ridge
Walvis Ridge
Walvis Ridge is an ocean ridge in the southern Atlantic Ocean, extending for thousands of miles, off the coast of southwest Africa. Both it and the Rio Grande Rise originated from hotspot volcanism now occurring at the islands of Tristan da Cunha , 300 kilometres east of the crest of the...
, and in the southwestern 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...
off Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
. These records suggest that it may have a circumglobal distribution in the Southern Hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...
, inhabiting subantarctic
Subantarctic
The Subantarctic is a region in the southern hemisphere, located immediately north of the Antarctic region. This translates roughly to a latitude of between 46° – 60° south of the Equator. The subantarctic region includes many islands in the southern parts of the Indian Ocean, Atlantic Ocean and...
waters and cold ocean current
Ocean current
An ocean current is a continuous, directed movement of ocean water generated by the forces acting upon this mean flow, such as breaking waves, wind, Coriolis effect, cabbeling, temperature and salinity differences and tides caused by the gravitational pull of the Moon and the Sun...
s, including the Benguela
Benguela Current
The Benguela Current is the broad, northward flowing ocean current that forms the eastern portion of the South Atlantic Ocean gyre. The current extends from roughly Cape Point in the south, to the position of the Angola-Benguela Front in the north, at around 16°S. The current is driven by the...
and the Humboldt
Humboldt Current
The Humboldt Current , also known as the Peru Current, is a cold, low-salinity ocean current that flows north-westward along the west coast of South America from the southern tip of Chile to northern Peru. It is an eastern boundary current flowing in the direction of the equator, and can extend...
. This species occurs in the open ocean between the surface and a depth of 502 m (1,647 ft), in water 830–4000 m (2,723.1–13,123.4 ft) deep.
Description
The largest known specimen of the longnose pygmy shark is a male 37 cm (14.6 in) long. Its body is slender and moderately compressed from side to side. The long, bulbous snout comprises about half the head length, and comes to a blunt, conical tip. The eyes are large, lack nictitating membraneNictitating membrane
The nictitating membrane is a transparent or translucent third eyelid present in some animals that can be drawn across the eye for protection and to moisten it while maintaining visibility. Some reptiles, birds, and sharks have a full nictitating membrane; in many mammals, there is a small...
s (protective third eyelids), and are followed by large spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
s. The nostrils are long and angled, with a very short flap of skin on their anterior rims. The mouth is transverse and surrounded by thin, smooth lips. The upper teeth number 22 rows and are small and upright with a single narrow cusp. The lower teeth number 23 rows and are much larger, broader, and knife-like, and interlock to form a continuous cutting surface. The five pairs of gill slit
Gill 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 tiny and of uniform width.
The two 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...
s lack spines. The first dorsal originates over the pectoral fin bases; the second dorsal is slightly larger than the first but is about equal in base length, and originates over the middle of the pelvic fin bases. The pectoral fins are short and somewhat paddle-like. There is no anal fin. The caudal fin is broad, with a well-developed lower lobe and a deep ventral notch near the tip of the upper lobe. The small dermal denticles have sharp wedge-shaped crowns bearing median ridges, and are placed on stalks (pedicels). This species is dark brown, with prominent blackish, then light bands at the fin margins. The underside is covered by minute light-producing photophore
Photophore
A photophore is a light-emitting organ which appears as luminous spots on various marine animals, including fish and cephalopods. The organ can be simple, or as complex as the human eye; equipped with lenses, shutters, color filters and reflectors...
s.
Biology and ecology
The natural history of the longnose pygmy shark is poorly known. It probably feeds on pelagic fishes and invertebrateInvertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s, and is presumably aplacental viviparous with a small litter size like other members of its family. The 13 cm (5.1 in) long type specimen had an umbilical scar, suggesting that it was close to the birth size. Males and females attain 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 under 36 and 33 cm (14.2 and 13 in) long respectively.
Human interactions
Only six specimens of the longnose pygmy shark are known to science. Its small size and oceanic habits appear to preclude its capture by most fisheries. Coupled with its wide distribution, this species does not seem threatened by human activity and has been listed under Least ConcernLeast Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
by the International Union for Conservation of Nature (IUCN).