identification - a small crab?

[supperouge]

hello,
this is the new friend I've found on my Briareum. It looked like some algae but it started moving.

Do you know this species? do you think I should keep it?
I've sps and a couple of lps in my small aquarium.

Thank you for helping me out!
Antonio

 

[Ron_Vas]

Looks kinda like an emerald crab

 

[homegrowncichlid]

looks sponge like, very interesting.

 

[supperouge]

looks sponge like, very interesting.

Yes, it was hard to recognize it. It really looked like a piece of sponge or algae when it was all closed on the coral