The Frilled Shark Has a 3-Year Pregnancy Before Giving Birth

The frilled shark has a long, eel-like body that can grow up to 6.5 feet (2 meters) in length. The body is dark brown or gray, with a cylindrical shape that tapers into a flattened tail. Its name comes from the six pairs of frilly gill slits that line its throat, giving it a distinctive, prehistoric look.

Unlike most sharks, the frilled shark has no separate dorsal fin near its tail. Instead, its pectoral fins are small and located closer to the head. It does possess a large anal fin and smaller pelvic fins on its backside to help propel it forward.

It also has a wide mouth lined with rows of needle-like teeth, perfectly suited for grabbing slippery prey.

There are two known species of frilled sharks: the common frilled shark (Chlamydoselachus anguineus) and the Southern African frilled shark (Chlamydoselachus africana).

The common frilled shark swims through a variety of deep-sea locations worldwide, including the Western Indian Ocean. By contrast, the Southern African frilled shark more often makes its home in the Atlantic Ocean.

Though similar in appearance, these species have subtle differences in their range and body structure. For instance, the common frilled shark has shorter gill slits, and its Southern African counterpart has both longer gills and a shorter head.

Both are equally rare and elusive, making them a challenge to study.

Frilled sharks are solitary animals, spending most of their time near the ocean floor. They're ambush predators, lying in wait for prey to swim by. Because of the isolated nature of this species' natural habitat, they are rarely observed interacting with other sharks or marine life.

Unlike many surface-dwelling sharks, frilled sharks do not form schools or display social behaviors. Their lives in the deep are largely solitary and focused on survival. They're loners whose hunting prowess hardly makes solo swimming a handicap.

This eel-like shark is a carnivore, feeding primarily on squid, fish, and other deep-sea creatures.

They have rows of sharp, backward-facing teeth that help them grab and hold onto slippery prey. Once they catch a meal, they swallow it whole, all thanks to their flexible jaws. They don't really need to lure prey, considering their speed and ferocity.

Their diet reflects their deep-sea habitat, where prey can be scarce. Frilled sharks have adapted to make the most of any hunting opportunity, sometimes targeting prey larger than themselves. It may be hard to be a frilled shark, but it's even harder to be one of its prey and escape!

Frilled sharks live at depths of 1,500 to 5,000 feet (500 to 1,500 meters). For perspective, the ocean floor is at around 12,000 feet (3,700 meters) on average.

They prefer cold, dark waters near continental shelves and upper slopes, where they can hunt for prey in the shadows. This species has been found in oceans worldwide, including off the coasts of Japan, Australia and Namibia.

Living so far below the surface, frilled sharks rarely encounter humans, which adds to their mystery. Their deep habitats provide them with protection from most predators, but it also makes studying them difficult.

Frilled sharks have an incredibly long gestation period — possibly up to three and a half years. That's the longest of any vertebrate. This slow reproduction rate is one reason why frilled sharks are so hard to come across. They also have a distinct breeding season, as opposed to being able to breed year-round.

Female frilled sharks give birth to live young, typically 6 to 12 pups at a time. The pups are fully formed miniatures of adults and must fend for themselves immediately after birth.

Frilled sharks are not currently classified as endangered, but their deep-sea habitats make it hard to estimate their population.

They are occasionally caught as bycatch in deep-sea fisheries, which could pose a threat to their numbers. Climate change and deep-sea mining may also impact their habitats in the future.

We created this article in conjunction with AI technology, then made sure it was fact-checked and edited by a HowStuffWorks editor.