what are these?

[jsdean]

I was looking at my tank tonight and there were a bunch of little guys running around on the bottom of my tank. They scurry around like ants, but look kind of like a shrimp. They dont swim and are just a few millimiters long. Any ideas? I have had my tank around 2 months and have 55lbs live rock. 56 gallon tank.

 

[dsa_mom]

http://web.odu.edu/sci/biology/jrh/whatis.htm
see if this link works.

 

[jsdean]

Thanks! thats definitely them. I also found this link:
http://www.allsands.com/Science/Anim...ods_vdh_gn.htm
Are they a bad thing for my tank?

 

[bang guy]

They are great! for your tank. They are very nutritious food and they clean up leftover food. What could be better?
From your first description I thought you were referring to Mysid Shrimp or Munnid Isopods, they more closely resemble ants. But if you've found a pic that matches then they must be Amphipods: