Help identifying creature.

[faebit]

I'm attaching an image of a critter that has appeared in one of our tanks. Its the very tiny green thing just below the pink acan. This thing will pull in whenever there is motion around it and when a shadow cast over it. The tank is a bit of a mess so getting a good shot of it proved difficult. I can post more images if needed.

 

[DaJMasta]

Sort of difficult to see in the image, but if you mean the sort of ring of feathers (like the tail of a shuttlecock), it's probably a small feather duster worm.