@farmerman,
I always thought that plaice and sole and flounder were separate species of flat fish but mebbe I'm wrong about that.
Anyway we use all three terms here.
Do you all know why halibut have squinty (asymmetric) eyes?
It's because the young are not bottom-dwellers, they swim in midwater like other fishes at first.
Later, they move to live out their adult lives on the bottom (until fm catches them, that is) and start swimming on their side. The bottom eye then migrates onto the top of the head, and the end result is the reason there are no mirrors down there.