Are you talking about the tube looking things that seem to be made out of sand? (actually they are made out of sand..lol)
I have to assume it is is either a small worm or snail (similiar to a vermetid) that makes these. I took a number of them out of my 120 last night when I was cleaning but didn't see the critter responsible.
They are harmless and common and often found on the bottom of your live rock in an established tank...if that is the question
..unless they are snail eggs...like Tahl said, a better pic would help