Is this a sponge ?

[FMF0331]

The long grey thing between the rocks

 

[Pedro Nuno Ferreira]

It looks very much to be a sponge ...

 

[ScorpionSys]

Looks like one to me too

 

[Pedro Nuno Ferreira]

sponges are not easy or may not be easy to identify as far as what species it is ... and usually they are good for the reef system and are a sign of good biological health ... however there is one sponge that is not good as it may overgrow everything and anything and destroy ... the black sponge ... now this is not to scare you and don't just pick up a sharp blade and remove it ... just keep and eye on it and if you notice that it grows fast and overgrows the vicinity, then remove it ...

Pedro Nuno:fish:

 

[ZANYMASTER]

Looks like a index finger

 

[FMF0331]

E.T 's finger.... Happy birthday Nelson, may the force be with you

 

[guri]

its a sponge it grows 4 or 5 inches like fingers and stops growing i like it,it looks very nice in my tank,later color will be black,they sting if you touch them with ur hand but on fingers you will not feel it dont bother corals dont grows very fast really god for landscaping

 

[jdnumis]

sponge!