Stonefish are a group of horrifying poisonous fish that lurk in the coastal waters of the Indian and Pacific Oceans. Named for their stone-like camouflage, they’re equipped with needle-like spines capable of secreting venom that, in some species, can be lethal even to humans.
Now, a new study has revealed that stonefish have another fearsome and unique defense mechanism: specialized bones on the cheek just below each eye socket which work essentially like switchblades.
The new research—which was conducted by scientists from the University of Kansas (KU) and the Field Museum in Chicago—has been published in the journal Copeia.
According to analysis of various specimens, the stonefish can control the spine-like bone, dubbed the “lachrymal saber,” so that it extends outwards horizontally like a strange mustache or sits flush against its face, as well as other angles in between. The researchers think this feature, in addition to its other venomous spines, could help the stonefish avoid being eaten.
“If you find pictures of these stonefishes in the mouths of other things, the lachrymal saber is always locked out,” William Leo Smith, an associate professor of ecology and evolutionary biology at KU said in a statement.
The researchers found that the deployment of this switchblade bone involves an unusually large number of specialized modifications to bones, muscles and ligaments in the cheek area.
Smith first became aware of the switchblade locking mechanism around 15 years ago while dissecting a stonefish that had been his pet. Since then, he has been trying to confirm exactly how the mechanism worked.
But switchblade bones, venomous spines and stone-like camouflage are not the only unusual features of stonefishes.
“A lot of them have really bright pectoral fins on sides of their body, and when they’re scared they flash them—this drab fish will suddenly flash bright yellows and oranges,” Smith said. “I always assume all of these features are defensive, but recent studies by other fish scientists suggest these could all be displays like a peacock.”