The 22-inch-long (56-centimeter-long) fetus has a single, functioning eye at the front of its head—the hallmark of a congenital condition called cyclopia, which occurs in several animal species, including humans.
Earlier this year fisher Enrique Lucero León legally caught a pregnant dusky shark near Cerralvo Island (see map) in the Gulf of California. When León cut open his catch, he found the odd-looking male embryo along with its nine normal siblings. "He said, That's incredible—wow," said biologist Felipe Galván-Magaña, of the Interdisciplinary Center of Marine Sciences in La Paz, Mexico.
Once Galván-Magaña and colleague Marcela Bejarano-Álvarez heard about the discovery—which was put on Facebook—the team got León's permission to borrow the shark for research. The scientists then x-rayed the fetus and reviewed previous research on cyclopia in other species to confirm that the find is indeed a cyclops shark.
Cyclops sharks have been documented by scientists a few times before, also as embryos, said Jim Gelsleichter, a shark biologist at the University of North Florida in Jacksonville. The fact that none have been caught outside the womb suggests cyclops sharks don't survive long in the wild.
Overall, finding such an unusual animal reinforces that scientists still have a lot to learn, Gelsleichter added.
"It's a humbling experience to realize you ain't seen it all yet."