thumb|Closer view of the head

The frilled shark (Chlamydoselachus anguineus), also known as the lizard shark, is one of the two extant species of shark in the family Chlamydoselachidae (the other is the southern African frilled shark, Chlamydoselachus africana). The frilled shark is considered a living fossil, because of its primitive, anguilliform (eel-like) physical traits, such as a dark-brown color, amphistyly (the articulation of the jaws to the cranium), and a –long body, which has dorsal, pelvic, and anal fins located towards the tail. The common name, frilled shark, derives from the fringed appearance of the six pairs of gill slits at the shark's throat.

The two species of frilled shark are distributed throughout regions of the Atlantic and the Pacific oceans, usually in the waters of the outer continental shelf and of the upper continental slope, where the sharks usually live near the ocean floor, near biologically productive areas of the ecosystem. To live on a diet of cephalopods, smaller sharks, and bony fish, the frilled shark practices diel vertical migration to feed at night at the surface of the ocean. When hunting food, the frilled shark curls its tail against a rock and moves like an eel, bending and lunging to capture and swallow whole prey with its long and flexible jaws, which are equipped with 300 recurved, needle-like teeth.

Taxonomy and phylogeny

The zoologist Ludwig Döderlein first identified, described, and classified the frilled shark as a discrete species of shark. After three years (1879–1881) of marine research in Japan, Döderlein took two specimen sharks to Vienna, but lost the taxonomic manuscript of the research. Three years later, in the Bulletin of the Essex Institute (vol. XVI, 1884) the zoologist Samuel Garman published the first taxonomy of the frilled shark, based upon his observations, measurements, and descriptions of a –long female shark from Sagami Bay, Japan. In the article "An Extraordinary Shark" Garman classified the new species of shark within its own genus and family, and named it Chlamydoselachus anguineus (eel-like shark with frills). Initially, marine scientists considered the frilled shark a living, evolutionary representative of extinct groups of elasmobranchs (rays, sharks, skates, sawfish), because the shark's body featured primitive anatomic traits, such as long jaws with trident-shaped, multi-cusp teeth; amphistyly, the direct articulation of the jaws to the cranium, at a point behind the eyes; and a quasi-cartilaginous notochord (a proto-spinal-column) composed of indistinct vertebrae. Nonetheless, the systematic biologist Shigeru Shirai proposed the Chlamydoselachiformes taxonomic order exclusively for the C. anguinesis and the C. africana species of frilled sharks. In 2009, marine biologists identified, described, and classified the Chlamydoselachus africana (southern African frilled shark) of the Atlantic waters of southern Angola and of southern Namibia as a species of frilled shark different from the Chlamydoselachus anguineus identified in 1884. The recorded, maximum body-length of a male frilled shark is , and the recorded, maximum body-length of a female frilled shark is . which suggested that the sharks lived inland, in shallow bodies of water far from the ocean. The shallow-water frilled shark had larger, stronger teeth, suitable for eating mollusks; scarcity and plenty of food are indicated in the tooth's morphology of sharper points (cusps) oriented into the mouth. From the Late Paleocene epoch (66–56 mya) until the contemporary era, other species of sharks out-matched the Chlamydoselachus sharks in competition for feeding grounds and living space, which restricted their geographic distribution to the deep-water ocean. Regarding the frilled shark's survival of the mass-extinction event which occurred at the Cretaceous–Paleogene time-boundary, one hypothesis proposes that the sharks survived in bodies of shallow water, both inland and on the continental shelf; afterwards, the frilled shark migrated to deep-water habitats.

Diet

The frilled shark eats a diet of cephalopods, Nudibranchs, smaller sharks, and bony fish;

thumb|alt=The head of a preserved shark, with the large mouth open|The frilled shark is a predator with long jaws directly articulated to the cranium, at a point behind the eyes.

In hunting and eating prey that are tired or exhausted or dying (after spawn), When the embryo is long, the mother shark expels the egg capsule, at which developmental stage the frilled shark's external gills are developed.

In 2016, consequent to the depletion of food sources caused by commercial overfishing of the feeding areas of the shark's deep-water habitat, and because of the shark's slow rate of reproduction, the International Union for the Conservation of Nature (IUCN) classified the frilled shark as a fish species under near-threat of extinction, and then reclassified it as a species of Least Concern of extinction.

See also

  • List of sharks

References

  • ABC News video
  • Chlamydoselachus anguineus, Frilled shark at FishBase
  • Deep Sea: Frilled Shark at ReefQuest Centre for Shark Research
  • Frilled Shark - Video at Check123 - Video Encyclopedia