Goblin shark

3 years ago by in Systematics and Taxonomy, Systematics and Taxonomy

1The goblin shark (Mitsukurina owstoni) is a rare, poorly understood species of deep-sea shark. Sometimes called a “living fossil”, it is the only extant representative of the family Mitsukurinidae, a lineage some 125 million years old. This species looks unlike any other shark, with an elongated, flattened snout, highly protrusible jaws containing prominent nail-like teeth, and pink coloration. It is usually between 3 and 4 meters (10 and 13 ft) long when mature, though it can grow considerably larger. Goblin sharks inhabit upper continental slopes, submarine canyons, and seamounts throughout the world at depths greater than 100 m (330 ft), with adults found deeper than juveniles.
Various anatomical features of the goblin shark, such as its flabby body and small fins, suggest that it is sluggish in nature. This species hunts for teleost fishes, cephalopods, and crustaceans both near the sea floor and in the middle of the water column. Its long snout is covered with ampullae of Lorenzini that enable it to sense minute electric fields produced by nearby prey, which it can snatch up by rapidly extending its jaws. Small numbers of goblin sharks are unintentionally caught by deepwater fisheries. The International Union for Conservation of Nature (IUCN) has assessed it as Least Concern, citing its wide distribution and low incidence of capture.

Taxonomy

American ichthyologist David Starr Jordan described the goblin shark in an 1898 issue of Proceedings of the California Academy of Sciences, recognizing the peculiar fish not only as a new species but also a newgenus and family. He based his account on an immature male 107 cm (42 in) long caught in Sagami Baynear Yokohama, Japan. The specimen had been acquired by shipmaster and naturalist Alan Owston, who had given it to Professor Kakichi Mitsukuri at the University of Tokyo, who in turn had brought it to Jordan. Thus, Jordan named the shark Mitsukurina owstoni in honor of these two men. The common name “goblin shark” is a translation of its old Japanese name tenguzame, a tengu being a Japanese mythical creature often depicted with a long nose and red face. Another name for this species is elfin shark.

Shortly after Jordan’s description was published, several scientists noted the similarity between Mitsukurinaand the extinct Mesozoic shark Scapanorhynchus. For a time, the prevailing view was to treat Mitsukurinaas a junior synonym of Scapanorhynchus. Eventually, more complete fossils revealed many anatomical differences between Scapanorhynchus and Mitsukurina, leading modern authors to again regard them as distinct genera. Several goblin shark specimens were described as separate species from 1904 to 1937, none of which are now considered valid. This taxonomic confusion arose because the specimens’ jaws were fixed at varying degrees of protrusion during preservation, giving the appearance of proportional differences in the head.

Biology and Ecology

Although observations of living goblin sharks are scant, its anatomy suggests that its lifestyle is inactive and sluggish. Its skeleton is reduced and poorly calcified, the muscle blocks along its sides (myomeres) are weakly developed, and its fins are soft and small. Its long caudal fin, held at a low angle, is also typical of a slow-swimming shark. The long snout appears to have a sensory function, as it bears numerous ampullae of Lorenzini that can detect the weak electric fields produced by other animals. Due to the snout’s lack of rigidity, it is unlikely to be used for stirring up prey from the bottom as has been proposed. Vision seems to be less important than other senses, considering the relatively small optic tectum in the shark’s brain. Yet unlike most deep-sea sharks, it can change the size of its pupils and thus probably does use its sight in some situations. Goblin sharks may fall prey to the blue shark (Prionace glauca). Parasites documented from this species include the copepod Echthrogaleus mitsukurinae, and the tapeworms Litobothrium amsichensis and Marsupiobothrium gobelinus.

Range of the goblin shark

Range of the goblin shark

Feeding

The goblin shark feeds mainly on teleost fishes such as rattails and dragonfishes. It also consumes cephalopods and crustaceans, including decapodsand isopods. Garbage has been recorded from the stomachs of some specimens. Its known prey includes bottom-dwelling species such as theblackbelly rosefish (Helicolenus dactylopterus), and midwater species such as the squid Teuthowenia pellucida and the ostracod Macrocypridina castanea rotunda. Thus, the goblin shark appears to forage for food both near the sea floor and far above it.

Since it is not a fast swimmer, the goblin shark may be an ambush predator. Its low-density flesh and large oily liver make it neutrally buoyant, allowing it to drift towards its prey with so few motions as to avoid detection. Once prey comes into range, the shark’s specialized jaws can snap forward at incredible speed to capture it. The protrusion of the jaw is assisted by two pairs of elastic ligaments associated with the mandibular joint, which are pulled taut when the jaws are in their normal retracted position; when the shark bites, the ligaments release their tension and essentially “catapult” the jaws forward  while the well-developed basihyal (analogous to a tongue) on the floor of the mouth drops, expanding the oral cavity and sucking in water and prey.

Life history

Little is known about goblin shark reproduction because a pregnant female has yet to be found and studied. It likely shares the reproductive characteristics of other mackerel sharks, which areviviparous with small litter sizes and embryos that grow during gestation by eating undeveloped eggs (oophagy). The birth size is probably close to 82 cm (32 in) the length of the smallest known specimen. Males mature sexually at approximately 2.6 m (8.5 ft) long, while female maturation size is unknown. No data are available on growth and aging.

Re love ution