Isopod How Do I Know

[atmmachine816]

So yesterday when I woke up and turned the lights on shortly after I saw a flat black bug zoom around my tank on the substrate running into the wall, digging into the sand and finally stoping under a rock where it was dark. I looked at lynden's link and it looks similar to a aegid but sounds a lot like a sand skater possibly. It was black, round, similar shape to a pill bug but didn't have any any legs or antenas, just the body shape round was similar. I haven't seen it since and was wondering if this is something to be worried about? Then on isopods all my little bugs are really tiny and hard to distinguish really what they are so are they mostly copepods or amphipods then?

thanks

 

[SkiFletch]

Some amphipods can look like pill bugs... Really tough to say without a pic

 

[atmmachine816]

And there's no way to get a pic I haven't seen this thing again since the time it was zooming around the tank for all of 10seconds. It seems like they are mostly harmful to fish and shrimp so when I do get a fish should I monitor it very closely along with my shrimp right now?