Mantis shrimp? ID please...

[chjy69]

While doing my regular maintenance job, I found these inside of my Aqua Clear 110 power filter.
They were inside of media chamber and even inside of huge sponge block!!!
I catch them, but do not know anything about them.
So I took a pic to figure them out.
Are they mantis shrimps?
Then do I have to catch them to take out of my tank?
They are less than 1/2" long...
Please help...

p.s.: There are tons of lives coming with live rocks... although they're free... I am very confused...:eek2:

 

[helipilot]

Looks like either copepods or maybe amphipods. Quite desirable in a reef tank.

 

[DanInSD]

Amphipods. Good food for small mantis...

 

[justinl]

+1 for the above. not a mantis at all. they'll reproduce in your tank and eat algae. beneficial.

 

[chjy69]

I just release them back into my tank, instead of releasing them into my aqua clear filter chamber.
By doing this, they will increase in numbers due to large volume of live rock (30lbs in 20G tank).
Thank you guys!