worm(?) id for a beginner..

[[pj]]

i have had my tank set up for about 2 weeks now. i got 4 fish and 4 rocks from a friend.
I was just checking out the tank in the dark with a flashlight and saw some things i did not expect to see. Little grey crawly things, almost like rolly pollies but lighter in color. they wer running in and out of the holes in the rocks and i think the were just out to feed.
Any idea what these are? good or bad?

 

[karlas]

what u have are amphipods they are very good for your tank they provide a natural food for you fish and are great scavengers they eat the detris off of the rock and sand in your tank the more the better here is a pic is this what u have?
amphipods

 

[[pj]]

yep...thanksfor the quick reply.
glad to know its good for the tank.