WHAT in the WORLD?! ID THIS!!!

I just saw this little guy in my tank, its about the size of a fat grain of rice and looks like a med size Rolly Polly (Pill bug).
It has a tail kind of like crayfish, shrimp and lobsters (Thought it was a baby mantis at first.
Its a light brown/cream color and has lots of tiny little legs.
What can it be? It looks like it has four tiny antennae (two going forward and two bending back towards its body) and it swam pretty fast when I tried to syphon it out.

 

Ok, I know it's an Isopod, but can anyone tell me if its harmful or beneficial?
I've looked on a few sites and some say its a pest while others say its a good addition.

 

great for sumps if thats what it actually is. Looks like a male isopod. I wouldn't see how they would be a problem in a reef. My sump is full of them along with copepods, amphipods and mysis.

 

Some isopods are parasitic, most are not. If you see it on one of your fish, then you know what kind you have.

 

It looked more like some of the parasitic ones rather than the peaceful ones. Didn't want to chance it so it's in toilet heaven now.

 

trust me, if you found one, there is more.

 

It came in the Macro I just bought. How do I kill them if theres more?

 

Not sure why you would want to. Almost all reef tanks have them, they are similar in size and personality as an amphipod. Wrasses and mandarins will eat them, along with all of your other pods too. They are a great addition to any tank and readily reproduce. Free food for your fish.

some reading for you....IsopodFAQs

 

Because she's not sure if it's a parasitic isopod. I would rather be safe than sorry myself.

 

Have you ever come across a parasitic isopod? Hers looks exactly like a sphaeromatid, which are harmless. I have a lot of these things in my sump and some in my display I'm sure.

The only ones I hear about often are the ones that eat fish tongue, actually they replace the fish tongue. Has no negative affect on fish though.

The main parasitic ones found in seawater (most parasitic are actually freshwater) are cirolanids, yours is a sphaeromatid. The cirolanids are very easy to distinguish from a sphaeromatid.

Some more reading for ya....Pills, Parasites, and Predators; Isopods in the Reef Aquarium by Ronald L. Shimek, Ph.D. - Reefkeeping.com