Tests confirmed the fish is the first vertebrate known to have developed mirrors to focus light into its eyes, the team reports in Current Biology.

"In nearly 500 million years of vertebrate evolution, and many thousands of vertebrate species living and dead, this is the only one known to have solved the fundamental optical problem faced by all eyes – how to make an image – using a mirror," said Professor Julian Partridge, of Bristol University, who conducted the tests.

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