Is this a sponge or what?

[cascardo]

Hello, there. I am new to the forum and new to reefing (I have a 60L nano for one and a half year only). I appreciate any help here.

So, I got this dark grey thing growing on my rock. Once, an invertebrate was passing by, and I had the impression it was moving or maybe just floating.

Is this a sponge or something like that? Can you help me to identify it? Should I keep or remove it?


Thanks a lot.
Cascardo.

 

[Gumbies R Us]

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