New growth on rocks

[firstsalttank91011]

First let me apologize if this is the wrong thread to post this, if there's a better one please let me know.

A few weeks ago we noticed some odd growth on a rock shaded by another rock. Depending on the light it has a yellowish look. I've included 2 pictures (which i wish were better quality and will try with another camera if needed).

Curious if anyone has an idea what this could be and any follow ups like if we should remove it, leave it, etc.

As always, appreciate everyone's time and replies!

 

[moz71]

Looks like sponge

 

[firstsalttank91011]

Looks like sponge

Where does it come from? We have a Sea Star as well and it just appeared. Any way to confirm it’s a sponge?

 

[Gatorpa]

Sponge.

They come on any live rock..