As shown in the image above: This "soldier fish" (a cloud-striped naked-skinned squid) has a lacrimal gland knife on each side of its head.
If you invite this stingered stonefish to a party, you know: it will carry two "switchblades" and cannot pull these thorns out because the weapons are embedded in its skull.
Scientists recently discovered these switchblades, also known as "tear gland knives," in a group of stonefish. Stonefish is a rare and dangerous fish that lives in the waters off the Coast of the Indo-Pacific.
William Leo Smith, deputy director of the University of Kansas Biodiversity Institute and Natural History Museum and principal investigator of the study, said: "I don't know why this hasn't been discovered before, it's probably because only one or two people have ever worked on this team." ”
All of the stonefish Smith analyzed had a unique "spring knife" device on their cheeks, just below the eyes.
As shown in the picture above: Scorpora, with knife-shaped eye socket bones.
Smith, an associate professor of ecology and evolutionary biology at the University of Kansas, said: "The lacrimal glands of this fish are usually immobile, but the lacrimal glands of this fish can rotate 90 degrees along the head-tail axis. ”
Essentially, when the spine is activated, it sticks out from the side, like a dangerous beard.
This spinning tear gland knife has a lot of spines on it, indicating that these fish use it as a weapon. When it is not in use, the tear gland knife rests on the fish's head, safely pointing backwards and downwards.
However, when the fish enters the "protected area", it pulls the palate with the muscles on the cheeks (usually used for chewing), thus rotating the spine through a circular, multiform locking mechanism.
Both male and female stonefish have lacrimal knives. Depending on the individual, the length of these barbed knives varies from half the width of the fish's eyes to 2.5 times the width of the eyes. In general, the knives of large stone fish are relatively small, while the knives of small stone fish are relatively large.
As shown in the image above: Long spiny scaly squid with knife-like eye fossa bones.
A species called the Australian scaly scorpion even has a knife that emits a terrible green color due to biofluorescence. The knife absorbs the light and then re-emits it at a lower wavelength. The researchers wrote in the study that during a dramatic light show, the rest of the fish's head glowed red.
The discovery took 15 years. It all started in 2003, when Smith was dissecting a stone fish he kept as a pet, and he quickly became the first scientist to understand how the spring knife construction worked anatomically.
The switchblade, while useful, is just one of many defenses that stonefish may use against predators. Others include spikes, camouflage, and some of the world's most powerful venoms that can even kill an adult.
Smith said in a statement: "Of all the fish I've studied, I haven't been stung by these stonefish. Indonesia has a large aquaculture industry, which is really unbelievable to me. Venom breaks down in our digestive system. But people all over the world eat a lot of poisonous species. ”