What would this be.....

[Boolay1978]

I came down to my tank during the night and put the light on and there was a white worm looking thing about an inch long swimming really fast round the tank then went behind a rock and disappeared.... Any ideas???

 

[EriksFish315]

Could of been a worm.

 

[Lionfish210]

Could be a flatworm. Was it flattish