Therefore I set to and re-wrote a merman's scene only to be surprised to learn, they aren't who I thought they were either.
No matter how I tried, they just weren't plausible enough to be who I intended them to be. So I let, the character tell, the White Queen, in his own words who he is and what he and his Lewellian mermen are all about. Turns out they are another order entirely and he even managed to secure their survival in the later novels. What a merman.