Another Creepy Crawlie - What's This One?

[Winterlily]

I'm fairly new to the world of live plants, so am not used to all the various......creatures..... that come along with them. Just did a water change and gravel vac and in the bucket afterward was this thing. TINY - about maybe 2-3mm. Looking like a worm and seeming to move like a worm. But I'm totally paranoid about leeches and anything else that could harm the fish. If it matters, it curls up in a ball when lifted from the water, if that means anything to you. It also seems to move sorta straight, not inchworm-y. I did read (again!) the plant hitchhiker thread that's pinned here, but don't see anything that looks like this exactly?

What is this thing and need I worry about it? Thanks!

(Sorry for not great pic - but it's TINY and this is the best I could do...)

 

[Winterlily]

Anyone??

 

[howard_hopkinson]

It looks like some sort of Planarian(flat worm) to me. If it is, then it should be harmless.

 

[drobbyb]

I vote planaria as well.

 

[keenonfish]

Yeah every tank has them nothing to worry about!

 

[Winterlily]

Great, thanks guys!

How does one tell the difference between these harmless guys and something like a leech - or is the latter something I really don't even have to worry about?