Small, clear, soft tubes. Are they a bad thing?

[amandah]

Hello all!

So I have spent the last 2 hours searching hitchhiker guides, forum posts, images, etc. for these guys that are in my tank. I cannot decide what they are. I found an exact match on one post, but ultimately no one could decide what they were. I am hoping you all can help me out.

Noticed these about 4 days ago. They are small white tubes. Soft and there are no feather duster tops coming out. When touched they don't do anything. The seem to grow mostly in shady areas, but some are out in the light. Only on two of my live rocks (which also have some green algae growth). I have had the rocks in my tank for over a year now and never noticed these before. Did have a huge and healthy cleaner shrimp in the tank who recently died (of old age I believe, she was getting huge and I had her for a long time). Could she have been taking care of these for me all this time and now that she's gone I am finally getting to see them?

Any help would be appreciated!

They are the white tubes center in the image and they run down to the right.
http://i.imgur.com/36gzI.jpg

 

[Petrichor]

I have a small pocket of those in my tank too. It's a type of sponge. Harmless and beneficial. I wanna say the name is spaghetti sponge, but I'm not sure if that's the official name.

 

[amandah]

Thanks for the id! I looked that up and found the scientific name (leucosolenia nautilia) and that's exactly what it looks like. I am glad it's not something bad that I need to exterminate.