Are these sponges or ?

[ReefAtlas]

I noticed a large group of these white / clear tube like "things" growing on the stalk of a hammer coral. The hammer does not seem to mind them yet. Are they a problem or just a strange sponge? Of course I was worried they were hydroids, but they do not look like any of the pictures I have found. The hammer is about 14 months old and is very healthy. No other known problems in the reef other than a small number of benign flatworms that won't go away.

 

[KJ]

Sponge.

 

[Lovemyreef2015]

+1 sponge. Harmless filter feeder