Can anyone please identify these critters

[Memo]

Can anyone please identify these critters I was looking in to my tank at night with a flashlight and there was approximately 15-20 of these critters swimming around like mad and attacking the sand and live rock. I have a 110 [acronym:1237e854ca="Gallon"]gal[/acronym:1237e854ca]. Tank with 120 lbs of live rock (Tonga and Marshal Island). Tank is been running since mid November. All parameters OK and have one small lionfish. They don’t bother the fish but they are swimming around and almost attacking the sand. What are they and do I need to get rid off them? They are attracted to the flashlights beam and I don’t see them during the day. Please help!
Thanks
Memo

[Memo]

Photo 2

[zenn]

Looks like a pod to me. And you DO NOT want to get rid of them if that's what they are. They are beneficial and a sign of healthy water conditions. They help with natural filtration of the water...not to mention a source of live food for your fish.

[demodiki]

That kind of looks like an isopod to me. Opinions?

[Fluff]

It does look like some type of isopod. Though, I've never seen anything like it. For the most part, isopods aren't anything to be concerned about. There is some parasitic ones but most are just janitors. Here are some links to photos of different types. Not an inclusive list I'm sure but shows some of the diversity in shape and size. So long as they don't appear to be a threat to anything in your tank, I'd say live and let live.

http://www.yale.edu/inverts/caribs/isopods.html
http://www.mov.vic.gov.au/crust/isopogal.html

[flamingonhot]

lloks like an iso.

Some are parasitic but they rarely get into tanks. The only ones that i've seen that are parasitic don't look yours so it's probably okay to leave it.
Most parasitic oones are a short round little things with giant black eyes spots.