Weird fish of the week: Frilled shark

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This week's weird fish caused a sensation back in January 2007, when video footage was released of a strange, snake like shark found swimming off the coast of Japan by a local fisherman.

The bizarre, alien looking fish featured was described on TV reports as a "living fossil" and its weirdness was enhanced by its oddly arched body shape, languid swimming style and gaping mouth filled with equally bizarre looking teeth.

It was captured and taken to a nearby marine park but unfortunately died shortly afterwards. Experts identified the fish as a Frilled shark, Chlamydoselachus anguineus.

The species is a relatively scare and seldom seen deep sea shark which usually only appears as by-catch from deep sea trawlers so has hardly ever been seen alive, but the images flashed across the world from this discovery are not exactly a true picture of this odd shark as the fish shown is clearly sick and near death. You can see the video footage below:

Despite these reservations they are still a good candidate for weirdness. Their long, almost eel-like bodies are not typical of what most people would consider shark-shaped and give them a look something like a stretched dog fish (Scyliorhinidae).

Their dorsal fin is small and situated far back near the tail, which is itself lacking the caudal notch associated with sharks.

They have exceptionally long jaws which are terminally positioned, rather than underslung like in the majority of shark species. These jaws are filled with lines of fine, tricuspid (three pointed), teeth. This combination of large mouth and fine teeth is believed to help them eat large prey, which once in the shark's mouth is unable to wriggle out again because of this hook-like dentition.

Stomach contents of captured specimens have shown that they appear to largely eat squid, fish and other smaller sharks. They get their common name from their distinctive frilly gill structure which is also a clue to their ancient lineage as they have six gill openings while 'modern' sharks have only five. Their scientific name is equally descriptive, 'chlamys' being Greek for cape/tunic/frilly and 'selachos' for shark, while 'anguineus' is from the Latin for snake-like.

Frilled sharks grow to around 2m maximum, with females being larger than males.

They are aplacental viviparous, the embryo's living inside eggs and hatching inside the mother at around 8cm then living off their yolk sac and also possibly gaining further nutrition in unknown ways from their mother until they are born at around 50cm long.

Litters are typically between two and 15. It has been speculated that the gestation period may last as long as three and a half years which would make it the longest of any vertebrate. This slow reproduction in combination with very limited knowledge of the species and an increase in deep water fishing has led them to be listed as 'Near Threatened' on the IUCN red list for endangered species.

In 2009 an ROV operating on the Blake Plateau off the south-eastern United States captured the first footage of the frilled shark in its natural environment which gives a better insight into how these fish look when alive and well.

A second, smaller species of frilled shark, Chlamydoselachus africana was described in 2009 and is found off the coast of southern Africa.

Why not check out some of our other Weird fish of the week features? 

Mega mouth shark

Flying gurnard

Pinecone fish

Sea lamprey

Slender snipe eel

Tripod fish

Lumpsucker

Ocean sunfish

Two-headed arowana

Stargazers

Giant oarfish

Kroyer's deep sea anglerfish

Halimeda ghost pipefish