What is this in my tank?

[dude23455]

there is some kind of slug in my tank. I dont know if its bad or not. Not sure where it came from, must have been attached to something I bought at the LFS recently.
Should i just leave it alone or remove it?

 

[brainrush]

Congrats you have a Sea Hare! They are REALLY good algae eaters. If you don't have lots of algae, though, or a really big tank, you should probably sell him. He will starve to death in no time.
Some people will pass them from tank to tank to clean up everyone's tank on the block and keep them from starving.
I think his horns look like Shrek! I had one and that was his name...

 

[reefkprz]

looks like a limpet maybe? does it have a flatish shell or is it bare back?

 

[threed240]

It's hard to see, but It looks bare back. It really does look like a sea hare.