Unknown hitchhiker

[JoeyPB]

I just noticed this little fellow on my glass this morning. I have no clue what it is. Perhaps some sort of slug?

Here is a video:
YouTube - ‪Saltwater Tank‬‏

 

[JoeyPB]

After looking around some, I'm pretty sure it's just a white flatworm now.

 

[iDream]

looks almost like a copepod