Centroscymnus coelolepis

The Portuguese dogfish or Portuguese shark (Centroscymnus coelolepis) is a species of sleeper shark of the family Somniosidae. This globally distributed species has been reported down to a depth of 3,675 m (12,057 ft), making it the deepest-living shark known. It inhabits lower continental slopes and abyssal plains, usually staying near the bottom. Stocky and dark brown in color, the Portuguese dogfish can be distinguished from similar-looking species (such as the kitefin shark, Dalatias licha) by the small spines in front of its dorsal fins. Its dermal denticles are also unusual, resembling the scales of a bony fish. This species typically reaches 0.9–1 m (3.0–3.3 ft) in length; sharks in the Mediterranean Sea are much smaller and have distinct depth and food preferences. Relatively common, the Portuguese dogfish is an active hunter capable of tackling fast, large prey. It feeds mainly on cephalopods and fishes, though it also consumes invertebrates and cetacean carrion. This shark has acute vision optimized for detecting the bioluminescence of its prey, as sunlight does not reach the depths at which it lives. The Portuguese dogfish is aplacental viviparous, with the young provisioned by yolk and perhaps uterine fluid. The females give birth to up to 29 young after a gestation period of over one year. Valued for its liver oil and to a lesser extent meat, Portuguese dogfish are important to deepwater commercial fisheries operating off Portugal, the British Isles, Japan, and Australia. These fishing pressures and the low reproductive rate of this species have led the International Union for Conservation of Nature (IUCN) to assess it as Near Threatened. The first scientific description of the Portuguese dogfish was published by Portuguese zoologists José Vicente Barbosa du Bocage and Félix António de Brito Capello, in an 1864 issue of Proceedings of the General Meetings for Scientific Business of the Zoological Society of London. They created the new genus Centroscymnus for this shark, and gave it the specific epithet coelolepis, derived from the Greek koiloscode: ell promoted to code: el ('hollow') and lepis ('fish scale') and referring to the structure of the dermal denticles. The type specimen, caught off Portugal, has since been destroyed in a fire. One of the widest-ranging deepwater sharks, the Portuguese dogfish is patchily distributed around the world. In the western Atlantic, it occurs from the Grand Banks of Newfoundland to the U.S. state of Delaware. In the eastern Atlantic, it is found from Iceland to Sierra Leone, including the western Mediterranean Sea, the Azores and Madeira, as well as from southern Namibia to western South Africa. In the Indian Ocean, this species has been caught off the Seychelles. In the Pacific, this shark occurs off Japan, New Zealand, and Australia from Cape Hawke, New South Wales, to Beachport, South Australia, including Tasmania. The deepest-living shark known, the Portuguese dogfish has been reported at depths of 150 m (490 ft) to 3,675 m (12,057 ft) from the lower continental slope to the abyssal plain, and is most common between 400 m (1,300 ft) and 2,000 m (6,600 ft). This species is found deeper in the Mediterranean, seldom occurring above a depth of 1,500 m (4,900 ft) and being most common at 2,500–3,000 m (8,200–9,800 ft). The deep Mediterranean has a relatively constant temperature of 13 °C (55 °F) and a salinity of 38.4 ppt, whereas in the deep ocean the temperature is generally only 5 °C (41 °F) and the salinity 34–35 ppt. The Portuguese dogfish is essentially benthic in nature, though young sharks can be found a considerable distance off the bottom. There is depth segregation by size and sex; pregnant females are found in shallower water, above 1,200–1,500 m (3,900–4,900 ft), while juveniles are found deeper. There may be several separate populations in the Atlantic, and sharks in the Mediterranean and off Japan appear to be distinct as well. The Portuguese dogfish typically reaches a length of 0.9 m (3.0 ft) for males and 1.0 m (3.3 ft) for females, though specimens up to 1.2 m (3.9 ft) long have been recorded. Sharks in the Mediterranean are smaller, growing no more than 65 cm (26 in) long. This species has a flattened, broadly rounded snout that is shorter than the mouth is wide. The nostrils are preceded by short flaps of skin. The eyes are large and oval in shape, positioned laterally on the head and equipped with a reflective tapetum lucidum that produces a yellow-green 'eye shine'. The mouth is wide and slightly arched, with moderately thick, smooth lips and short furrows at the corners extending onto both jaws. The upper teeth are slender and upright with a single cusp, numbering 43–68 rows. The lower teeth have a short, strongly angled cusp and number 29–41 rows; their bases interlock to form a continuous cutting surface. The five pairs of gill slits are short and nearly vertical. The body of the Portuguese dogfish is thick and cylindrical except for the flattened belly. The two dorsal fins are small and of similar size and shape, each bearing a tiny grooved spine in front. The first dorsal fin originates well behind the pectoral fins, while the second dorsal originates over the middle of the pelvic fin bases. The pectoral fins are medium-sized with a rounded margin. There is no anal fin. The caudal fin has a short but well-developed lower lobe and a prominent ventral notch near the tip of the upper lobe. The very large dermal denticles change in shape with age: in juveniles, they are widely spaced and heart-shaped with an incomplete midline ridge and three posterior points, while in adults they are overlapping, roughly circular, smooth, and flattened with a round central concavity, superficially resembling the scales of bony fishes. Young sharks are a uniform blue-black in color, while adults are brown-black; there are no prominent fin markings. In 1997, a partially albino individual, with a pale body but normal eyes, was caught in the northeastern Atlantic. This represented the first documented case of albinism in a deep-sea shark. Living almost exclusively in the aphotic zone where little to no sunlight penetrates, the Portuguese dogfish is relatively common and the dominant shark species in deeper waters. The large, squalene-rich liver of this shark allows it to maintain neutral buoyancy and hover with minimal effort; males contain more squalene in their livers than females. A tracking study in the Porcupine Seabight has found that the Portuguese dogfish has an average swimming speed of 0.072 m/s (0.24 ft/s), and does not remain in any particular area for long. This species may be preyed upon by larger fishes and sharks. Known parasites of this species include monogeneans in the genus Erpocotyle, and the tapeworms Sphyriocephalus viridis, S. richardi, and Anthobothrium sp.