The longnose pygmy shark (''Heteroscymnoides marleyi'') is a rare

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of squaliform shark in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Dalatiidae The Dalatiidae are the family of kitefin sharks of the order Squaliformes (the term "kitefin shark" also refers specifically to the species '' Dalatias licha''). Members of this family are small, under long, and are found worldwide. They have ci ...

and the only member its

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

. It is known only from a handful of specimens collected from the cold

oceanic Oceanic may refer to: *Of or relating to the ocean *Of or relating to Oceania **Oceanic climate **Oceanic languages **Oceanic person or people, also called "Pacific Islander(s)" Places * Oceanic, British Columbia, a settlement on Smith Island, ...

waters of the Southern Hemisphere, between the surface and a depth of . Reaching 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 A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through c ...

s of nearly equal size, with the origin of the first lying over the

pectoral 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 ...

bases. The longnose pygmy shark does not appear substantially threatened by fisheries, and has been assessed as

Least Concern A least-concern species is a species that has been categorized by the International Union for Conservation of Nature (IUCN) as evaluated as not being a focus of species conservation because the specific species is still plentiful in the wild. T ...

by the

International Union for Conservation of Nature 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 nat ...

(IUCN).

Taxonomy

The longnose pygmy shark was described by American

zoologist Zoology ()The pronunciation of zoology as is usually regarded as nonstandard, though it is not uncommon. is the branch of biology that studies the animal kingdom, including the structure, embryology, evolution, classification, habits, and d ...

Henry Weed Fowler in a 1934 volume of ''Proceedings of the Academy of Natural Sciences of Philadelphia'', based on a long female collected off Point Ocean Beach in

Durban Durban ( ) ( zu, eThekwini, from meaning 'the port' also called zu, eZibubulungwini for the mountain range that terminates in the area), nicknamed ''Durbs'',Ishani ChettyCity nicknames in SA and across the worldArticle on ''news24.com'' from ...

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...

. 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 Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

''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 Ocean The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by t ...

off eastern KwaZulu-Natal, in the southeastern

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

near the

Walvis Ridge The Walvis Ridge (''walvis'' means whale in Dutch and Afrikaans) is an aseismic ocean ridge in the southern Atlantic Ocean. More than in length, it extends from the Mid-Atlantic Ridge, near Tristan da Cunha and the Gough Islands, to the Africa ...

, and in the southwestern

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the contin ...

off

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

. These records suggest that it may have a circumglobal distribution in the Southern Hemisphere, inhabiting

subantarctic The sub-Antarctic zone is a region in the Southern Hemisphere, located immediately north of the Antarctic region. This translates roughly to a latitude of between 46° and 60° south of the Equator. The subantarctic region includes many islands ...

waters and cold

ocean current An ocean current is a continuous, directed movement of sea water generated by a number of forces acting upon the water, including wind, the Coriolis effect, breaking waves, cabbeling, and temperature and salinity differences. Depth contours ...

s, including the Benguela and the Humboldt. This species occurs in the

open ocean The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or wa ...

between the surface and a depth of , in water deep.

Description

The largest known specimen of the longnose pygmy shark is a male 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 membranes (protective third eyelids), and are followed by large spiracles. 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 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 and rays, as well as deep-branching vertebrates such as lampreys. In con ...

s are tiny and of uniform width. The two

s lack spines. The first dorsal originates over the

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 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 ...

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 A photophore is a glandular organ that 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, ...

Biology and ecology

The natural history of the longnose pygmy shark is poorly known. It probably feeds on

pelagic The pelagic zone consists of the water column of the open ocean, and can be further divided into regions by depth (as illustrated on the right). The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or w ...

fishes and

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

s, and is presumably

aplacental viviparous Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a term used as a "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparous reproduction. Ovoviviparous animals possess embryos that develop ins ...

with a small litter size like other members of its family. The long

type specimen In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes th ...

had an umbilical scar, suggesting that it was close to the birth size. Males and females attain

sexual maturity Sexual maturity is the capability of an organism to reproduce. In humans it might be considered synonymous with adulthood, but here puberty is the name for the process of biological sexual maturation, while adulthood is based on cultural definit ...

at under 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

by the

(IUCN).

References

{{Taxonbar, from=Q387836 Dalatiidae Fish described in 1934