Long, translucent tentacles eating LR "sand"

[gspeckman]

I've got two pieces of very porous live rock. Every now and then I will see a "poof" of what looks like fine sand, grey in color, come out of some of the small holes in the rock. As this "sand" accumulates either on the rock or the crushed coral substrate, a creature with very long, translucent tentacles kind of scoops the sand up with it's tentacles and brings it towards it's "mouth". I've never been able to actually see it's mouth though.
Two questions. 1. What is shooting out this fine sand from the holes in the LR and 2. what is the creature with long tentacles eating this stuff?

 

[OrionGirl]

1. Probably a worm of some kind, many live in holes in the rock. It's their waste that they don't want in their home.

2. Sounds like another kind of worm--there are many. Check here: http://reefs.org/hhfaq/

 

[mogurnda]

In addition to what OG mentioned, there are also boring clams and mantis shrimp that can dig into your live rock and leave sand piles.

I'll bet the tentacles belong to a terebellid (aka spaghetti) worm. The body stays hidden, while long, clear tentacles go hunting for debris.