A Deep Sea Merman, 1571

     As everybody knows, sea cows - the dugongs of Asia and Australia, and the manatees of Central and South America and the west coast of Africa - were the inspiration for the mermaid legend. They even bear the scientific name, Sirenia, "mermaids", although the classical sirens were bird-women rather than fish-women.
     Let me state, here and now, that this is not a fact, but a "factoid": something which "everybody knows", but is nevertheless false. If mermaids were really sea cows, they wouldn't be attribruted to the western coasts of the British Isles and northern Europe, or to Greece, where belief in them is (was) strongest. They would be treated as strange beings dwelling in distant parts - like the unicorn, which was based on garbled accounts of the Indian rhinoceros. But there is one thing both merfolk and sea cows have in common: they are creatures of the inshore shallows. One place you would never expect them would be the open Atlantic Ocean, with water more than a mile deep.