Flatworm predator?

[SweetLips]

Sorry the picture isn't great - but the brown tear-shaped thing that looks like tissue is actually a fairly large flatworm, not the little red/brown ones that explode in numbers. I tried to take a photo after it left the coral, but the autofocus didn't work too well, probably because of the water surface. I have posted it anyway - "gliding away" at least it shows the shape when extended
Water parameters are excellent: sg1.025, nh4 0, no2 0 no3 15ppm alk 3.8meq/l and ca 420ppm
Could be the flatworm is irritating the coral - it irritated me so it had to go.
I'm hoping the tissue recession will stop now.

Thanks again for everyone's input