Scientists recently discovered a two-headed shark among egg-laying species from the Mediterranean.
The finding of the peculiar Atlantic sawtail catshark embryo was detected among 767 embryos.
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According to National Geographic, researchers noted: "Each head had a mouth, two eyes, a brain, a notochord and five gill openings on each side. The two heads fused behind the gills.
"On the single body, there were four anticipated dorsal fins, two anterior, right and left and two posterior, right and left."
Experts say that animals with two heads have a difficult time sustaining themselves in the wild.
According to C. Michael Wagner, a biologist from Michigan State University, "If they make it to birth, two-headed sharks probably don't survive long in the wild...since they likely have a hard time swimming and finding food."
In 2013, a Florida fisherman got a surprise when he caught a bull shark - and found a live two-headed foetus inside the animal.
The fisherman released the other shark offspring, which were able to swim away, but kept the specimen and passed it on to scientists who described it in a study published by the Journal of Fish Biology.
According to discovery.com, Michael Wagner, co-author of the paper, said it is one of only six examples of a two-headed shark ever recorded, and the first time this has been seen in a bull shark.
He told The Register: "They're hardy little critters. But despite this, the two-headed specimen probably would have died after birth. It was near-to-term, but should have been a lot larger – the body looks to have invested so much energy in growing a separate head that the rest of the body was foreshortened."