Is this a type of Sponge?

[serpico1]

I have this growing on my rock. At first it was all flat, now I see tentacle like sprouts coming out of it. Is this a type of Sponge? if not, What is it?

 

[homer1475]

It's sponge. The "tentacles" are actually vent holes.

 

[duberii]

+1 and it's a cool sponge too

 

[ssunthar]

+1 and it's a cool sponge too

I have a similar one too... do we need to feed this guy? What they eat?

 

[duberii]

If it's growing then you're already doing something right- If you want it to grow more, there's a possibility that dosing silicates or phytoplankton would help, but they can also cause nutrient issues so I wouldn't mess with them unless the sponge is receding

 

[ssunthar]

If it's growing then you're already doing something right- If you want it to grow more, there's a possibility that dosing silicates or phytoplankton would help, but they can also cause nutrient issues so I wouldn't mess with them unless the sponge is receding

Thank you.