Green worm?

So I was looking at my tank tonight and I saw something totally new... It was a green worm-like thing coming out of the sand under a rock. It actually kind of looked like a snail's siphon but it kept stretching up out of the sand and onto a rock. It was flat but curved itself around into a tube and was "swallowing" grains of sand as it moved. I couldn't see any other identifying characteristics (segments, eyes, etc.) but it was very sensitive to light and would suck itself back into the sand super fast as soon as light hit it. I got really lucky and got this picture of it but I'm not sure how much it'll help as it pretty much has no identifiable characteristics...
Any ideas? Should I be concerned? Should try to get it out (if that's even possible...)? Thanks!

Isn't it so weird?! So I just looked at it again and to give an idea of size, I saw about 2 inches of it stretched out along the surface of the sand but clearly there's more below the sand. It's only about 1/16 of an inch wide though. It seems to keep the front part sort of flat to scoop up sand and the rest curved which carries the sand down towards the part that's under the sand (think conveyor belt... it's quite neat to watch the individual grains of sand moving along). It's not completely curved around to form a closed tube but mostly curved like in a u-shape to keep the sand in...

Thanks Reefkid! That definitely makes me worry less. Have you ever seen any more of the critter exposed other than the siphon-like thing? I wonder where it came from...