A gif of a ratfish coming out from behind a rock.
This image is only slightly NSFW (Picture: Metro.co.uk)

There’s no shame at all in having problems in the bedroom, but ‘sorry, my forehead teeth won’t get up,’ might be a new one.

Male ratfish, also called ghost sharks, live in the depths of the north-eastern Pacific Ocean and have bulbous green eyes, venomous spines and plates of teeth used to crunch the shells of clams and crabs.

They also have a fleshy rod inside a pocket above their eyes, a bit like the dorsal fin of an angler fish, covered in spikes.

Now researchers have discovered that these are actually teeth, complete with mineralised tips.

These gnashes, however, aren’t used for eating – this appendage, called a tenaculum, is for gripping a female’s pectoral fin during mating, new research has found.

Karly Cohen, a researcher at the University of Washington’s Friday Harbor Labs, who collaborated with the team, said scientists had never spotted teeth outside the mouth in this way before.

(Hydrolagus colliei) The Spotted Ratfish is a northeast Pacific Ocean species found from Alaska to Baja California. They are named for the pointed rat-like tail. Mature males have claspers on the underside of its body. Beware of the spine on the forward dorsal fin, if not handled correctly it will slice your hand.
Ratfish are known to scientists as Hydrolagus colliei (Picture: Getty Images)

Meet the ghostly ratfish that uses teeth on its forehead to have sex
The frontal clasper sits inside a pocket when not in use (Picture: PNAS)

She said: This insane, absolutely spectacular feature flips the long-standing assumption in evolutionary biology that teeth are strictly oral structure.

‘The tenaculum is a developmental relic, not a bizarre one-off, and the first clear example of a toothed structure outside the jaw.’

Gareth Fraser, a professor of biology at the University of Florida and senior author of the study, added: ‘If these strange chimaeras are sticking teeth on the front of their head, it makes you think about the dynamism of tooth development more generally.

‘If chimaeras can make a set of teeth outside the mouth, where else might we find teeth?’

To clarify, Fraser doesn’t mean ratfish are a chimaera, best known as a fire-breathing monster with a lion’s head, a goat’s body and a serpent’s tail.

Chimaera are cartilaginous fish like sharks, but lack many shark-like traits, like, well, sharp teeth or scales.

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Meet the ghostly ratfish that uses teeth on its forehead to have sex
We hope he’s got a good dental plan at work (Picture: PNAS)

But Fraser and his team wanted to know why ratfish actually have shark-like teeth, albeit ones on a club-like gripper used for sex.

So the researchers examined 40 ratfish specimens, with some over two and a half feet long, as well as fossils, according to the paper published in the Proceedings of the National Academy of Sciences.

By using micro-CT scans, they watched as the tenaculum grew over the ratfish’s lifetime from a tiny nub to a long rod used to give love bites.

Molecular tests identified tooth-forming genes in the appendage, which are typically found in the mouths of sharks.

One of the ghost shark’s ancient relatives, the Helodus simplex, which lived 315million years ago, also had a tenaculum stretching from its snout to its upper jaw.

This suggests that tenaculum teeth formed because of evolutionary tinkering or ‘bricolage’, said Michael Coates, a professor of biology at the University of Chicago.

Spotted ratfish (Hydrolagus colliei). Marine fish.
The rod is only present in male ghost sharks (Picture: Getty Images/iStockphoto)

‘We have a combination of experimental data with paleontological evidence to show how these fishes co-opted a preexisting program for manufacturing teeth to make a new device that is essential for reproduction,’ he added.

For Fraser, how a gnarly, not-a-shark shark with a toothy appendage that hooks mates came to be isn’t too surprising. It’s the depths of the ocean, after all.

From fields of wispy crimson worms to alien-like glowing snailfish that have never seen daylight, all sorts of life thrives in this dark, crushing environment.

‘There are still plenty of surprises down in the ocean depths that we have yet to uncover,’ Fraser said.

Get in touch with our news team by emailing us at webnews@metro.co.uk.

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