I do, there's a statue of her at my school. She was a robust and powerful figure, with the lower half of an octopus.

[Hoo boy he sure is cutting it very close to being a filthy liar here. Not that he minds, but lies are harder to keep track of than half-truths. And when if things do get out, no doubt she'll be rather cross with him over it.]

You know, it 's possible you may have them in your world was well. Unless the depths of your oceans have been explored, there's no way to know. Merfolk tend to be reclusive, and during the Sea Witch's era it was against the law to interact with humans.