Mysterious thing happening

[Reefrules1965]

I have a corkscrew she'll that has been sitting in the tank empty for months. All of a sudden it began getting rubble attached to it and has been accumulating more. It is only able to attach what is right next to it, it doesn't move around the tank. It has attached things at both ends. I never see any kind of critter. Anyone have an idea of what is going on?

 

[Ron Reefman]

Random small objects getting moved around by the flow in the tank to a 'dead spot' in the flow by that big rock?

I'd guess a hermit crab had moved into the shell, but you said it never moves.

 

[Reefrules1965]

I have moved the shell to several different places in the tank over the last three weeks and it always attaches more pieces wherever I move it. It's been a long slow process. They are being attached in a straight line. So, from both ends of the corkscrew shell the pieces are attached straight out.