Black slug-What is it?

[Ken-21]

I have these black slugs or shell less snails that roam my tank at night. From what I can see they don't hurt any corals and they can't grab any fish but I still would like to know what they are. I stink at computers and I tried to follow the instructions on how to post a picture but have failed. My son's very smart when it comes to computers so I'll eventually learn how to post pics. Anyway, does anybody have any idea what it could be?

 

[jimroth]

Probably an elephant slug aka keyhole limpet. Harmless/free cleanup crew. See if this looks familair:

http://www.seaslugforum.net/factsheet.cfm?base=scutus