Flatworm?

[Ultijekyll]

I have had this tank set up for 9 months and noticed these flatworm looking thigns on the front glass today... this tank only has a few basic mushrooms and GSP no fish currently.

What sort of flatworm are these

 

[KJ]

Acoel Brown Flatworms .

 

[vetteguy53081]

yes on acoel. Not the destructive but annoying as they multiply like mice eventually annoying corals, etc. daily vacuuming and sucking them up will reduce population.
Flatworm exit will work to rid of them but a lunare or melanurus wrasse should devour them too.