Cook's swellshark
Encyclopedia
The Cook’s swellshark is a little-known species
of catshark
, family
Scyliorhinidae, found in the Arafura Sea
at a depth of 223–300 m (731.6–984.3 ft). It is a stocky-bodied shark with a short, broad head and a large mouth, and can be identified by the eight dark, pale-edged saddles along its grayish brown body and tail. The maximum known length of this species is 30 cm (11.8 in). Like other swellsharks, it can inflate itself with water or air when threatened.
(CSIRO) publication. It is named in honor of the late shark
fishery
biologist and conservationist
Sid Cook. The type specimen is a 29 cm (11.4 in) long adult male collected from the Arafura Sea
.
, from the Northern Territory
of Australia
to the Tanimbar Islands
of Indonesia
. It resides in water 223–300 m (731.6–984.3 ft) deep.
s preceded by laterally enlarged flaps of skin that do not reach the mouth. The slit-like eyes are positioned high on the head and followed by tiny spiracle
s. The long, narrow mouth lacks furrows at the corners and contains 50–61 tooth rows in the upper jaw and 49–62 tooth rows in the lower jaw; each tooth has a long central cusp and a pair of smaller lateral cusps. The upper teeth are exposed when the mouth is closed. The fourth and fifth pairs of gill slit
s lie over the pectoral fin bases and are shorter than the first three.
The pectoral fins are rather small and angular, with nearly straight trailing margins. The two dorsal fin
s have rounded apices; the first is much larger and taller than the second, originating over the back half of the pelvic fin bases, while the second is positioned opposite the similarly-shaped but slightly larger anal fin. The pelvic fins are small and angular; males have very long claspers. The caudal fin is low, with a distinct lower lobe and a strong ventral notch near the tip of the upper lobe. The dermal denticles are widely spaced, with three points and a median ridge. The dorsal coloration is distinctive, consisting of a grayish brown background with six pale-edged dark saddles along the body and two on the tail. The first saddle is curved forward, with its front edge intersecting each eye. There are pale dots on the snout and fins, and inside the saddles on the body. On the flanks, the dorsal coloration fades into the plain light gray of the underside.
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 catshark
Catshark
Catsharks are ground sharks of the family Scyliorhinidae, with over 150 known species. While they are generally known as catsharks, many species are commonly called dogfish....
, 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...
Scyliorhinidae, found in the Arafura Sea
Arafura Sea
The Arafura Sea lies west of the Pacific Ocean overlying the continental shelf between Australia and New Guinea.-Geography:The Arafura Sea is bordered by Torres Strait and through that the Coral Sea to the east, the Gulf of Carpentaria to the south, the Timor Sea to the west and the Banda and Ceram...
at a depth of 223–300 m (731.6–984.3 ft). It is a stocky-bodied shark with a short, broad head and a large mouth, and can be identified by the eight dark, pale-edged saddles along its grayish brown body and tail. The maximum known length of this species is 30 cm (11.8 in). Like other swellsharks, it can inflate itself with water or air when threatened.
Taxonomy
The Cook's swellshark was described by Peter Last, Bernard Séret, and William White in a 2008 Commonwealth Scientific and Industrial Research OrganisationCommonwealth Scientific and Industrial Research Organisation
The Commonwealth Scientific and Industrial Research Organisation is the national government body for scientific research in Australia...
(CSIRO) publication. It is named in honor of the late shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
fishery
Fishery
Generally, a fishery is an entity engaged in raising or harvesting fish which is determined by some authority to be a fishery. According to the FAO, a fishery is typically defined in terms of the "people involved, species or type of fish, area of water or seabed, method of fishing, class of boats,...
biologist and conservationist
Conservationist
Conservationists are proponents or advocates of conservation. They advocate for the protection of all the species in an ecosystem with a strong focus on the natural environment...
Sid Cook. The type specimen is a 29 cm (11.4 in) long adult male collected from the Arafura Sea
Arafura Sea
The Arafura Sea lies west of the Pacific Ocean overlying the continental shelf between Australia and New Guinea.-Geography:The Arafura Sea is bordered by Torres Strait and through that the Coral Sea to the east, the Gulf of Carpentaria to the south, the Timor Sea to the west and the Banda and Ceram...
.
Distribution and habitat
The Cook's swellshark is only found in the Arafura SeaArafura Sea
The Arafura Sea lies west of the Pacific Ocean overlying the continental shelf between Australia and New Guinea.-Geography:The Arafura Sea is bordered by Torres Strait and through that the Coral Sea to the east, the Gulf of Carpentaria to the south, the Timor Sea to the west and the Banda and Ceram...
, from the Northern Territory
Northern Territory
The Northern Territory is a federal territory of Australia, occupying much of the centre of the mainland continent, as well as the central northern regions...
of 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...
to the Tanimbar Islands
Tanimbar Islands
The Tanimbar Islands, also called Timor Laut, are a group of about 65 islands in the Maluku province of Indonesia, including Fordata, Larat, Maru, Molu, Nuswotar, Selaru, Selu, Seira, Wotap, Wuliaru and Yamdena.-Geography:...
of Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
. It resides in water 223–300 m (731.6–984.3 ft) deep.
Description
A small species growing to 30 cm (11.8 in) long, the Cook's swellshark has a stocky body and a short, broad head. The snout is flattened and rounded, with the nostrilNostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
s preceded by laterally enlarged flaps of skin that do not reach the mouth. The slit-like eyes are positioned high on the head and followed by tiny 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 long, narrow mouth lacks furrows at the corners and contains 50–61 tooth rows in the upper jaw and 49–62 tooth rows in the lower jaw; each tooth has a long central cusp and a pair of smaller lateral cusps. The upper teeth are exposed when the mouth is closed. The fourth and fifth 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 lie over the pectoral fin bases and are shorter than the first three.
The pectoral fins are rather small and angular, with nearly straight trailing margins. 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 have rounded apices; the first is much larger and taller than the second, originating over the back half of the pelvic fin bases, while the second is positioned opposite the similarly-shaped but slightly larger anal fin. The pelvic fins are small and angular; males have very long claspers. The caudal fin is low, with a distinct lower lobe and a strong ventral notch near the tip of the upper lobe. The dermal denticles are widely spaced, with three points and a median ridge. The dorsal coloration is distinctive, consisting of a grayish brown background with six pale-edged dark saddles along the body and two on the tail. The first saddle is curved forward, with its front edge intersecting each eye. There are pale dots on the snout and fins, and inside the saddles on the body. On the flanks, the dorsal coloration fades into the plain light gray of the underside.