The frilled shark (Chlamydoselachus anguineus) is a truly remarkable creature, often called a living fossil due to its primitive features and the fact that it has changed very little over millions of years. These sharks are rarely seen by humans because they live in the deep ocean, typically near the seafloor on continental shelves and slopes, at depths of 500 to 1,500 meters. This deep-sea habitat, with its limited competition from other sharks, is one of the main reasons for their unchanging appearance.
Appearance and Anatomy
The frilled shark is an eel-like creature with a slender body that can grow up to two meters long. It has a dark brown or grey colour. Its most distinctive feature is the six pairs of gill slits, with the first pair wrapping around its throat, creating a frilly collar-like appearance, which gives the shark its common name. Other notable features include:
- A small dorsal fin, located far back on the body
- Small, paddle-shaped pectoral fins
- A large mouth at the front of the head, rather than a snout that extends over the mouth
- 300 teeth, arranged in about 25 rows, each with three sharp points like a mini pitchfork
The frilled shark’s body is adapted for life in the deep ocean, with a cartilaginous skeleton and a large liver full of low-density lipids to maintain buoyancy. Its lateral line system helps it detect movement and vibrations in the surrounding water. The species is also known for its snake-like movements as it swims in a serpentine fashion.
Diet and Hunting
These sharks are active predators, feeding primarily on deep-water squid and various fish, including other sharks. Their large mouth and flexible jaws allow them to swallow prey up to half their body length. Frilled sharks use their sharp, inwardly-pointing teeth to trap prey, and they may actively take prey that is over one and a half times their length. They may curl their bodies and lunge like a snake to capture prey, and sometimes lure prey with their bright white teeth in the dark depths.
Reproduction and Life Cycle
Frilled sharks are ovoviviparous, meaning the embryos develop within the mother’s uterus, nourished by a yolk sac, until they are born live. They do not have a placenta. The gestation period is remarkably long, thought to be from one to 3.5 years. A litter can range from 2 to 15 pups, which are born between 40 and 60 cm long.
Habitat and Distribution
Frilled sharks have a patchy distribution in marine waters around the world, usually in biologically productive areas such as upwelling zones. They are found in the Atlantic and Pacific Oceans, with populations off the coasts of Norway, Scotland, Ireland, Namibia, California, Chile, Japan, Australia, and New Zealand. They typically live close to the seabed at depths between 500 and 1,000 meters, but they can be found as deep as 1,500 meters, and sometimes as shallow as 50 meters.
Conservation Status
Although they are rarely observed, frilled sharks are not considered to be threatened. The International Union for Conservation of Nature (IUCN) has classified them as ‘Least Concern’. They are sometimes caught as bycatch in fisheries, but no fisheries specifically target them. Due to their deep-water habitat and slow reproduction, they are naturally rare.
Why Are They Called Living Fossils?
Frilled sharks are called living fossils because they have retained their primitive traits over millions of years, looking similar to their prehistoric ancestors. Their lineage can be traced back to the Carboniferous period, and some of their characteristics, such as their dentition, are reminiscent of cladodont sharks from the Devonian period. Their body shape and some features are similar to ancient sharks, having remained largely unchanged, with some scientists classifying them as part of the most ancient lineage of sharks.
The frilled shark is a fascinating creature that provides a glimpse into the deep sea and the ancient history of sharks. Its unique features and adaptations make it a truly remarkable species in our oceans.
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