Flatworm? Fluke?

[JW99]

A weird flat shaped thing crawling around on my glass. This is the only one I've seen. Any ideas on ID and if I need to remedy this? Don't think I have any livestock that would eat this currently.

 

[SouthwestAquaculture]

Looks like planaria. A quick Google and compare to confirm. They don't actually cuase harm until they proliferate to large numbers then they can smother certain corals. Wrasses or damselfish keep them in check. Chemical solution would be Flatworm exit. Read up on it before using. Good luck!