Feather duster dying or dead?

Hey there. Have had a feather duster now for about 3 months. It was doing great...water parameters have not changed. Everything is at zero. No changes in flow yada yada yada, the thing just will not come out of its tube anymore...I can see it down in there but thats it. I have some sexy shrimp and 2 scissortail dartfish and thats really it. Not sure what is causing it not to come out like this. Its been hiding now about 3 or 4 days. I picked it up out of the sand bed and flipped it upside down thinking maybe the dead worm would come out and gave it a little shake and nothing. So yeah, wondering what you guys think. It does look like it has fresh white along its tubing though that was under neath the sand. I dont know if thats because it was building more tubing or due to it not being exposed to the algae and what not to turn brown. Thanks guys and gals.