If it looks like a flying saucer, then it is actually not a pleco but a hill stream loach...otherwise a number of plecos have flatter body including vampire plecos...
I bought a couple different plecos that have a flatter body.
Labeled as vampire but of course not. The other was labeled tiger and has really thin light stripes going across it.
It might be under the Ancistrus sp. but not too sure.
The "vampire" is probably an L244 they have been avaiable from wholesalers which pet shops buy from. But if you really want to be sure put up some photos
The one on the rock is probably a king tiger the one that is far away and to the right is probably that L244 that I said earlier. With out any better pics can't do any better