Merpeople

Mrs. Rowling seems to have taken folklore of a variety of sea-folk and combined them into her own form of merpeople.¹ As such, the details on these folk sometimes contradict things you would expect having learned of them from more standard sources. Essentially one could posit that what we know of these creatures is a distorted view of the magical world caused by the confusion engendered by the Statute of Secrecy.

Merpeople, as a group, have rejected classification as beings despite fully qualifying for such status.² She seems to have split them into three races: Siren, selkies, and merrow; native to the Mediterranean, Scotland, and Ireland respectively.³ This fits well with what I read in a recent Tor article on the variety of mermaid myths around the world.⁴