The bighead spurdog (''Squalus bucephalus'') is a rare and little-known

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 ...

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

Squalidae 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 ...

. It is found in deep water south of

New Caledonia ) , anthem = "" , image_map = New Caledonia on the globe (small islands magnified) (Polynesia centered).svg , map_alt = Location of New Caledonia , map_caption = Location of New Caledonia , mapsize = 290px , subdivision_type = Sovereign st ...

, and over the Norfolk Ridge. Reaching at least in length, this stocky shark is brown above and light below, with a broad head and two

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 conv ...

s with long spines. It is the only member of its genus with both one- and three-pointed

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. An infrequent

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 ...

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 ...

, this species is listed under

Data Deficient A data deficient (DD) species is one which has been categorized by the International Union for Conservation of Nature (IUCN) as offering insufficient information for a proper assessment of conservation status to be made. This does not necessaril ...

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 natu ...

(IUCN).

Taxonomy

The first specimens of the bighead spurdog were collected during

South Pacific 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 continen ...

biodiversity Biodiversity or biological diversity is the variety and variability of life on Earth. Biodiversity is a measure of variation at the genetic (''genetic variability''), species (''species diversity''), and ecosystem (''ecosystem diversity'') l ...

surveys conducted by the Institut de recherche pour le développement (IRD). The species was described by Peter Last, Bernard Séret, and John Pogonoski in a 2007 Commonwealth Scientific and Industrial Research Organisation (CSIRO) publication. The

specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...

''bucephalus'' is derived from the

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

''bu'' ("large") and the Greek ''kephalis'' ("of the head"). Of the four original specimens, a long immature male caught over Norfolk Ridge was selected as the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

. Morphologically, this species belongs to a subgroup of ''Squalus'' defined by the shortnose spurdog (''S. megalops'') and the

Cuban dogfish The Cuban dogfish (''Squalus cubensis'') is a dogfish, a member of the family Squalidae in the order Squaliformes. Distribution and habitat It is found in the Western Atlantic from North Carolina to Florida, in the Gulf of Mexico, around Cuba, H ...

(''S. cubensis'').

Description

The bighead spurdog is a robustly built, spindle-shaped shark with a hump behind the head. The head is notably broad, and the snout is short and triangular with a blunt tip. The nostrils are preceded by a forked flap of skin. The medium-sized eyes are oval in shape and have a notch in the outside corner; behind them are small, crescent-shaped

spiracle Spiracle or spiraculum may refer to: * Spiracle (arthropods), opening in the exoskeletons of some arthropods * Spiracle (vertebrates), openings on the surface of some vertebrates * Spiraculum, a genus of land snails in family Cyclophoridae Cycl ...

s. The mouth is nearly straight and bears long furrows at the corners. There are 26–27 upper and 22–24 lower tooth rows. Each tooth has a single angled, knife-like cusp. There are 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, with the first four pairs small and the fifth pair longer. The two

s bear long spines and have narrowly rounded apexes, concave posterior margins, and short free rear tips. The first dorsal fin originates above 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 ...

insertions; the second is smaller than the first and originates behind 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. The pectoral fins are medium-sized with rounded tips, the pelvic fins are small, 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 ...

. There are lateral keels on the caudal peduncle. 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 se ...

is asymmetrical, with a long upper lobe and a well-developed lower lobe; the trailing margins of both lobes are convex. The skin is covered by tiny, non-overlapping

s. Unlike other ''Squalus'' species, adults have a mix of one-cusped and three-cusped denticles. This species is dark brown above, darkening towards the apexes of the dorsal fins, and pale below. The dorsal fin free rear tips and the caudal fin posterior margin are white. The largest known specimen measures in length.

Distribution and habitat

The bighead spurdog has only been recorded from the waters south of New Caledonia, and from

seamount A seamount is a large geologic landform that rises from the ocean floor that does not reach to the water's surface (sea level), and thus is not an island, islet or cliff-rock. Seamounts are typically formed from extinct volcanoes that rise abru ...

s on the Norfolk Ridge in the northern

Tasman Sea The Tasman Sea (Māori: ''Te Tai-o-Rēhua'', ) is a marginal sea of the South Pacific Ocean, situated between Australia and New Zealand. It measures about across and about from north to south. The sea was named after the Dutch explorer Abe ...

. It has been caught between the depths of .

Biology and ecology

Virtually nothing is known about the natural history of the bighead spurdog. Male appear to mature sexually at under long.

Human interactions

Small numbers of bighead spurdogs are caught incidentally by longliners fishing for ruby snapper (''Etelis carbunculus'') south of New Caledonia. The

(IUCN) presently lacks sufficient data to assess the conservation status of this species.

References

{{Taxonbar, from=Q5017919 bighead spurdog Fish of New Caledonia Taxa named by Peter R. Last Taxa named by Bernard Séret Taxa named by John J. Pogonoski bighead spurdog