it's an isopod. scroll through this guys post and you can see what he's been dealing with, waging war on those nasties. page 2 and 3 I believe contain pics of the isopods. http://www.nanotank.com/viewtopic.php?t=378&start=0
In the water it doesn't look to be as dark of a color as out of the water. In the water it's opaque white and light pink, kind of hard to notice against the coraline algae.
The last pic does kind of look like an amphipod..
I'm not taking any chances though. If I see the other on, and hopefully it's the only one, I'll KILL THE WABBIT!!!!!!!! KILL THE WABBIT!!!!!!!!!!