What is this thing, a slug or a flatworm?

[Logzor]

I found one of these crawling around on the glass and another on the rock. It lifted its body up to move, much like a snail does.

It was about 1 cm or less in size, much larger than the flatworms I have seen in my tank. It had some thickness to it also.

The color was transparent white.

If the img does not work:

http://logzor.deviantart.com/art/slug-69611569

 

[LeslieH]

An acoel flatworm, possibly a species of Convolutriloba. They eat copepods and micro-organisms.

 

[Logzor]

Thanks for the ID!

I wonder if it is bad for my tank, will it eat other flatworms? I have some of the tiny brown ones too.

 

[LeslieH]

These particular flatworms are harmless. They won't eat the brown flatworms unfortunately.

 

[madadi]

i had does in my tank and they eventually all died out.