ID of "growths"

I have noticed these new "growths" on the GSP mat. The GSP seem unaffected and fully bloom every day. I have another colony in the back right corner that do not have any of these growths. Can someone ID them. Any help is appreciated.

 

Kinda looks like some kinda sponge. Specially in the first pic....or maybe it's a.....I dunno, that's all I got. Good luck with the ID

 

I agree with sponges.

If the GSP is not unhappy - then I would say :

"if it aint broke, dont fix it!"

 

Looks like sponge siphons to me from the first pic.

 

O.k. Thanks all, sponge was the guess in another forum I am a member. I'll look into sponges, now I am curious as why they are popping up.

 

They look very odd to me, not quite a sponge. I have seen them before but can not remember the ID, I almost want to say a macro algae. The opening has me puzzeled.

 

They look cool. Hopefully they don't become a nuisance.

 

O.k. The plot thickens. The other colony I have does have some also. That colony hardly ever retracts but I was cleaning the glass today and disturbed it and when it retracted I saw a few there also. So now, the macro theory put forth by Corailline or some other polyp coral are definite possibilities along with sponge.

 

Try touching the hitchhiker and tell us what it feels like.

 

Listen here buddy! I'm not touching anything I don't know what it is!