Looks like a serpulidae to me, and if so, they're pretty cool, and more closely related to christmas tree worms I think.
I do NOT believe they can reproduce without another one present because the sexes are seperate. I believe the male and female release eggs and sperm into the water column, and then when the two meet, the stork shows up. I don't think a single specimen can reproduce though. If you have live rock, then there's a good chance you have another. He won't hurt the snail of course. Just watch the snail in case he dies, so you can put him in a nice spot.