I think your flounder may actually be a ray.

But I did see a flounder (wah) two weeks ago between Xtabi and Rockhouse.
Flounders tails end much closer to their bodies and their mouth is on the edge of their heads vs. a ray's which I believe is located on the underside of their bodies.
AND Flounders have a nasty disposition and definitely can bite.
They do have camo ability like the ray in the picture.

Ask Mrs. Peel, she was snorkeing with me and never did see the flounder.