For the first time, scientists have seen an egg-laying (oviparous) shark embryo with two heads.

It belongs to the species Galeus atlanticus, otherwise known as the Atlantic sawtail catshark.

This species now joins the list of real life two-headed creatures found in nature, which BBC Earth looked at in depth in October 2016.

The embryo was not easy to spot. It was hidden amongst 797 others, which the scientists had stored for medical research in their laboratory in Malaga, Spain.

Both sharks had a mouth, two eyes and even two brains. They also had two hearts, stomachs and livers, but shared an intestine. The two were attached below the gills.

Though other two-headed sharks have been found, they all belonged to species of shark that give birth to live young, such as the bull shark foetus discovered in 2013.

It is not known whether this two-headed shark would have survived if it had been born. Though, as the researchers write in the Journal of Fish Biology: "It is known that, although with a low incidence, two-headed conjoined twins occur in all major groups of vertebrates."

Melissa Hogenboom is BBC Earth's staff writer. She is @melissasuzanneh on Twitter.

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