Representational picture of a stonefishPhoto by Ian Waldie/Getty Images

Scientists have discovered a type of 'switchblade' mechanism on the face of stonefish, a rare venomous fish.

The lead researcher of the study, William Leo Smith, who is also the associate curator at the Kansas University Biodiversity Institute and Natural History Museum, said in a statement: "I don't [know] why this hasn't been discovered before. It's probably because there are just one or two people that ever worked on this group."

The stonefish can rotate the bone [the lachrymal] 90 degrees along the head-tail axis. These bones are used as a weapon and are heavily spiked.

When not in use, Smith says, the bone, which is pointed backward and down in a secured manner, rests against the fish's head. Whenever it is required, the fish uses its cheek muscles to pull on the upper jaw, which makes the spine rotate and the bone pokes out like a dangerous mustache, reported Live Science.

The study has been published in the journal Copeia in February.

Both the female and male stonefish, which live in the coastal waters of the Indo-Pacific, have these lachrymal sabers. However, the size differs depending on the individual. In general, smaller stonefishes have larger sabers, while larger ones have smaller sabers.

One species called the centropogon australis has lachrymal sabers that have a green glow because of biofluorescence, a mechanism by which organisms absorb light and then emit it as a different color.

"Of all the fishes I've studied, I haven't yet been stung by any of these stonefishes. There is an aquaculture for larger ones in Indonesia. That's mind-boggling to me. The venom breaks down in our digestive system. But people eat lots of venomous species all over the world, even in the US," says Smith.

The stonefishes are also masters of camouflage. They can sit still inside corals and rocky reefs with their bodies perfectly mimicking the surroundings while waiting to pounce on their prey. They also have powerful jaws and large mouths and able to swallow their prey whole, reported